I sell postal items, such as postcards, first day covers and postal history. My inventory is in the nice sturdy photo boxes you’d buy at Michaels or Hobby Lobby. I have different categories of items separated.
For instance my first day cover inventory is all by date order. I can find a cover instantly. I do have 10 year group marker cards to aid in this.

Same with my other categories such as postal history. Decade markers, then the items are just in random order. As my inventory grows, I will break it down to five year markers, and maybe even year markers. As inventory grew, I’d split out things like military related covers. Again, I can find stuff pretty fast.

I see other dealers resorting to inventory numbers, some even have these bar coded on clear plastic sleeves. I don’t have to go to that degree of organization or expense. I also have my mailers set ahead of time. Tonight I prepped 50 number 11 envelopes, and matching stiffener cards, all with postage attached.

Each morning I check my over night sales. 1-5 sales, even with multiple items per order, Pick the order from inventory. Hand address the envelope, enclose item(s) inside stiffener, stuff and seal. Done! I can easily fulfill those orders in minutes. And then I drop them at the post office on my way to work!