No matter how long the hike, you should always have a first aid kit handy. A FIRST AID kit is one of the 10 Essentials and you should customize its contents based off of your needs and trail conditions. One great way to put your first aid kit together is using a Nalgene bottle.
Not only does a Nalgene bottle offer a container that keeps your items dry, it also serves as an emergency water bottle if you find potable water on the trail or need to fill up and treat water you found in a stream. Nalgene bottles are lightweight, extremely durable, BPA free and leakproof. This makes it an ideal container.
At a bare minimum, your day-hike first aid kit should have:
Band aids (or gauze and medical tape)
Moleskin (for blisters or hot spots)
Antibiotic ointment
Anti-itch treatment
Ibuprofen or acetaminophen
From there, you will need to evaluate your personal needs. Do you wear contacts? You may want to put a bottle of eye drops in there. Do you tend to roll your ankle? Pack some athletic tape. Do you get sinus headaches from allergies? Have at least two doses of decongestant. As you make your kit, think about those things that you need to treat your body specifically in case something happens on the trail.
Another thing to consider is the conditions of the trail. If you know are going to be exposed to the sun for long periods on the hike, you may want to pack sunburn relief gel (aloe vera) and oral rehydration salts (in case of dehydration). If you are hiking in wet conditions, pack extra moleskin and bandages (wet feet blister more easily) as well as hand/foot warmers.
Other items you may want to consider adding to your kit:
Antiseptic wipes or hand sanitizer
Biodegradable soap
Liquid bandage
Butterfly bandage
Throat lozenges
Tweezers
Trauma scissors
Do some research on what first aid items you would like to pack in your kit and put them all into your Nalgene bottle. Educating yourself on wilderness first aid and the many tools in pre-packed kits is a good thing to do so you aren’t scrambling in times of emergency.
Remember, packing a first aid kit is not just a one-time process. You should check it before every trip to ensure that you have enough supply of each item (especially if you had to dip into it on your last hike), to check ointment and medication expiration dates, and so you remember what you have in your kit. You'll be glad you took the time to prepare if you have to use the First Aid Kit.