Tents, tents, tents. The great benefit of making sets of Single-Sprew Tents in many designs is that almost everyone would buy many boxes of each. Tents are useful for many eras world-wide.
BUM has done well doing this. I've got the generic (pup-tents) in White, Blue, Gray and Butternut to go with my ACW, Victorians, Roman Forts, WWI, etc. I've got the round ones for my Knights and Sudan (pushing it but nothing better yet). Atlantic got too expensive to keep looking for them on Ebay. Same with good TeePees in their nice, truely soft plastic.
KEEP IT SIMPLE - TENTS (TEE-PEES) ONLY. To me, the problems with BUM, Imex and the other sets of Accessories, is that you have to get all the other stuff in the same box that you don't need nor want. The extra stuff in fact discourages me, not encourages me, to buy any at all, or at least some.