Some ideas for a first aid kit is sterile gauze pads, band-aids, non-latex gloves different sizes, dependant upon who could use it, best to keep all sizes or a couple sets of a larger size , antibiotic, hydrocortisone cream, a breathing barrier (for CPR), and a reference card. The card should have emergency numbers burn control, poison control, EMS, family members .
You can build a first aid kit specified for your needs. The suggestions listed above would be best for a smaller kit that you could carry around, however if you want a large kit add in a flashlight which extra batteries , a blanket, scissors, thermometer, hot/cold pack two different packs, you break and they heat or cool , and elastic wraps. Basically, you can put whatever you want in a first-aid kit. Just make sure if you have medications, etc. in it you restock it and check it regularly. You need to check the dates to be sure that there are not expired materials in the kit.