I’ve talked a lot about Tourniquets. The two best on the market, and really the only two you should consider are the CAT-7 and the SOFTT WIDE gen 3 or 4. A five minute youtube video will show you how to use it and they are durable enough that you can practice applying them hundreds of times and you won’t hurt them.
Watch out for counterfeit tourniquets, and order from a reputable source, like Rescue Essentials (not Amazon).
Other than that it depends on how big your kit is and how much you want to spend. Hemostatic gauze is nice, but expensive, has a short shelf life, and is really only needed for certain applications.
I’ve heard people say that Benedryl will reduce the severity of a major allergic reaction. It’s certainly not as effective for anaphylaxis as an epi-pen, but it’s inexpensive, is something you can carry around all of the time and is much better than nothing.