Depend on the items. I do a sale alternating years and do one in spring nad one in fall. Most of the spring stuff gets saved for fall-already priced and I box everything up and stack in garage so it doesn't have far to go in the fall.
Then after the fall sale, I really only keep what I think will sell well later-like the bigger ticket items, and kids stuff in good shape. Adult clothing always gets donated as it takes up too much room and never gets the same good prices as kids' clothing. I usually save kids items (take them to the children's resale place and then box up any leftovers they don't take that are still in good shape-our resale place will sometimes not take if they deem they have an "abundance" of a certain item).
I try to label the boxes really well and stack them how I would organize them for the sale (one stack might have a box of shoes, a box of adult accessories, a box of adult jewelry, etc...) Especially with kids stuff, I put sizes on them-occasionally, I'll run across someone who is in need and I can pull an entire box and give it to them (I know it's bad, but I have an easier time passing stuff on to friends than to Goodwill as not sure how much of it actually gets put to use)