Being an EMT for 20+ years I have gone over and over what supplies I should have, best place to buy and prices to buy them at. I STILL have that debate with myself after all these years and have tried to discipline myself...hehheehe with no luck.
When it comes to prepping I feel like a kid in a candy store.
What I have found and this is personal opinion only, is that there are a few basics that you should have:
2", 4'" and 6" gauze rolls
4x4 gauze pads
5x9 gauze pads
Trauma pads
Large Kerlex rolls
2" and 4" coban rolls....these are better than tape because it sticks to itself and not you

Crazy glue is great for cuts, stings like the dickens but works.
Assorted bandaid sizes.
Isopropyl Alcohol
plain white pillow cases are good also to use for slings, banadages and "other" things
Plenty of different sized safety pins
Splinting supplies should be a consideration also.
I don't know what your level of First Aid is, but these are usuable by most everyone and a good start to a "general" first aid kit.
All these supplies can be bought in bulk and I bought everything at Family Dollar, Dollar General, Big Lots and of course EBAY. Looks like others have also listed good purchase points too...I will have to check these out. I have found also that plain old tackle boxes work great to keep these things out of the weather and mobile. What I don't keep in tackleboxes, I keep in cardboard boxes...still mobile and I can mark everything. Hope this helped some.
We sleep soundly in our beds because rough men stand ready in the night to visit violence on those who would do us harm. - Winston Churchill