Well we probably have half a dozen first aid kits and didn't really think about what happens when the medicines (and even bandages!) expire. Seems like there has to be a better way of getting the right set of refills. While you could individually get the various parts and also medicines, it is nice to have them all sealed up. Especially the meds.
Anyway, here's what the research shows for the various kits we have including

• Adventure Medical Kit 2.0. This is a great basic kit. It is pretty heavy, but designed for 1-4 people on a day hike. We use for our cars
• REI Hiker Kit. Another useful kit
• Ikea. They have a basic kit, the best thing is the bright color
• Red Cross First Aid. This is a bigger home kit.
• Ultralight/Waterproof. Have never used these in practice, but have a few.

Adventure Medical Kits. We have the 2.0 version which is for 1-4 people on a day. It is actually very nice and we use it in the cars. And they do have refill kits, but it is hard to find even on Amazon. They do have their own direct site, so you can get what you need including. It's sad to see that the base kit costs $22, so that you pretty much buy the kit again when you refill. On the other hand, you rarely need the complete refill set except for medications which do expire: • • Medications, Backpacking.$5.95. The common stuff. We can use for
• Topical Antiseptics and Ointments. $4.95. Very useful to prevent infections. Much like the REI kit below but probably 2x the stuff. • Bandages and Dressing, Mountain.$7.95. Tape and so forth. It doesn't have regular bandages
• Wound Cleaning and Closing. This seems a little optional

REI also has refill kits and they are a little less expensive. A little hard to tel how equivalent, but they have

• REI Wound Cleaning Refill Kit. $3. Thjis gives you wipes and antibiotic ointment • REI Minor Wound Care Refill Kit.$4.50. These are the basic bandages and gauze pads.
• REI Cohere Wrap. This is nice for wrapping your blisters. $4.50 • REI Zonas Tape. To tape this up$4.
• REI First-Aid Medications Refill. \$4.50. The basic advil and so forth.

So in the end to refill a standard kit