We should all try to clean whatever containers we don't want and bring them to the next swap. Some folks didn't bring the correct containers or any containers at all. I know it sounds like a pain to do that, but we can collectively do better to reduce our impact of the wasteful plastic in this hobby.
I know @Srt4eric has plenty of space for empty cups in his truck.
If you write the info on printer labels or label tape rather than on the plastic it’s a lot easier for the recipient to reuse them. And usually easier to read.