PACK - Packs are sized by the amount of liters they can hold.  We recommend a 25 to 35 liter pack with a decent frame.  We started out with very small 10 liter packs and quickly realized that they were not adequate, and also uncomfortable even with very little weight because they did not have frames.  We quickly moved to 35 liter packs, that we have even used on warm weather overnight trips.  Barbara loves her Osprey, and Oscar loves his Lowe Alpine.   In addition to liter capacity, they are also sized to fit various torso lengths.  Make sure that you choose a pack sized  to fit you. Two other features we think are important are:  1) Water reservoir system (we find we drink much more if we use a water reservoir pouch with a tube that runs out of our packs, and we always carry minimum 3 liters with us) and 2) Rain covers.  Many packs have both these features included.  If not, we recommend you buy them to work with your pack.  

FOOTWEAR - This is extremely dependent on the terrain you are hiking in, and your personal preference.  For day hiking, since you are not carrying a lot of weight, you generally should not need heavy duty hiking boots.  However, if like us, you prefer something with ankle stability and some support, lighter weight boots are a good option.  Be sure to buy them about a size larger than you normally wear to allow for swelling.  We didn't do this at first, and ended up selling our first set of boots within a month or so of buying them.  The brands we have worn and love areLowa Renegade GTX and Keens.  We also sometimes hike in trail shoes or trail runners, if we know that we are on a trail where we don't think there are a lot of rocks or snakes!  Many hikers hike only in this style of lighter weight shoe.  Two other items to consider for your feet are insoles and socks.  We always buy a better insole to put into our boots to provide better arch support than the manufacturer supplied insoles.  Barbara prefers the very sturdy Superfeet brand, while Oscar prefers the more cushioned SofSole.  This is a significant additional investment after you buy shoes, but the health of your feet are critical if you want to enjoy hiking.  For socks, we strongly recommend merino wool because they stay comfortable, don't get smelly like other materials, don't tend to cause blisters, and keep you warm even if wet.  Smartwooland Fits are our two favorite brands.  

APPAREL - Dress for the weather, but be sure to include layers.  If you are hiking in areas with elevation changes in particular, a hot day can quickly become cold and windy, or rainy.  Even when we leave dressed for a hot summer hike, we take a merino wool or polyester performance fabric (capilene, polartec, etc) shirt, and a rain jacket or poncho with us, at minimum.  If we are expecting weather changes, we take other wool or down jackets as appropriate.  For sun protection, we always wear hats that shade our face and necks as well, and usually have a light weight long sleeve option.  As a rule, we do not wear any apparel made of cotton, because it tends to chafe and if you get sweaty and then get cold, cotton will make you colder.  We stick to merino wool or quick drying performance clothing depending on our activity and the temperatures.  

FOOD AND WATER - Our water reservoirs hold 3 liters, so we always take 3 liters minimum.  If we are going on longer or hotter hikes, we add one or two liter nalgene bottles to make sure we have enough water.  Water is not something to skimp on, especially if you are hiking where there are no water sources.  We always take the food we plan to eat for the day (including some salty snacks such as nuts or jerky), as well as two or three extra bars such as Clif bars.  These are light-weight insurance, and have a long shelf-life.  Remember that if you are hiking all day, you can easily burn 3000 or more calories, so be sure to take adequate food. 

SURVIVAL GEAR - Even if we are taking a "walk in the park", we never leave home without:

     - Compass and a printed map of the area where we are hiking.  The map may be a copy of something from a ranger station or book, or an actual map.  We never             rely solely on electronic GPS or phone for navigation.  If you hike remote, less traveled, poorly marked trails take a better map, of course.  

     - Knife - we prefer a multi-tool type knife such as a Swiss Army Knife or Leatherman, but even a basic pocket knife is invaluable.

     - Whistle to signal for help if needed - make sure it is somewhere accessible and not at the bottom of your pack!

     - Basic first aid kit with bandages, antibiotic cream, benadryl, pain relievers, and blister care.  You can buy them pre-packed, or make your own in a small                            waterproof pouch.  If you make your own, you can "cheat" and look at contents of a pre-made kit!  Taking a basic wilderness first aid course is also a great idea.

     - Headlamp or flashlight - we prefer a headlamp because you can use it hands-free if you need to hike in the dark.  We like the Black Diamond Spot for day hiking             since it is very light, inexpensive, and only for emergencies.

     - Fire-starting tools - we carry a lighter as well as a small emergency magnesium fire starter and a small tin or pill bottle with cottonballs soaked in vaseline.

     - Water purification - you can either carry chemical or mechanical water purifiers.  Something small and light.  You don't need one that will pump out a large                     volume, just something you can use in an emergency.    

     - Emergency blankets - we carry the small foil-looking emergency blankets in case we are stuck overnight and need heat

     - Duct Tape - we carry some wrapped around our lighters, and around a pencil.  You can wrap a little around anything so you always have some.

     - Sunscreen and chapstick

TREKKING POLES - While not required, we have found that we strongly prefer hiking with our poles to ease the load on our knees, and aid in balance, especially in "sketchy" situations like creek crossings, or steep slopes where it helps to have added balance.  Choose an option with a foam or cork handle, and flick locks (not screw locks).  We have had great luck with our Black Diamond poles.  

HIKING GEAR:  Although you may only be going on a short day hike, it's important to be prepared.  Many of the stories we hear about people who have to be rescued, or lose their lives outdoors, are day hikers that were unprepared.  We pack light for day trips, but we always travel with some essentials that we believe would allow us to survive overnight.  There are options for every budget, and many items can be purchased already made or you can assemble them yourself, such as first aid kits.  We have found local hiking shops or other local outdoor retailers to be very helpful in educating us about gear.  We have also found REI to be a great source of good quality gear and assistance.  They also put on classes (some free) that cover hiking topics. If you know what you want, a good on-line source of quality gear is Moosejaw.  Here is what we use, as an example, if you are just getting started.  Please note, we are not experts!  We just started hiking seriously in 2014, and learned from attending seminars, talking to lots of people, and a lot of trial and error.  We hope this summary of our experience might help others have a few less errors!