I scouted things out at Dollar Tree today. Here's some things that might come in handy for the current swaps or those coming up...
Dry Erase Markers, 4 pack
Popsicle Sticks, 125 pack
Large Foam Shapes, 24 pack
Tweezers, 2 pack
Number Sticker Strip, 75 pack (I think. It's in a roll in the teachers section.)
Small/Medium Food Storage Containers, 4 pack (if I remember right)
Clothespins, 36 pack (I think)
Those ice cream bowls pictured in the spooning bead post by Walking By the Way. Don't know how budget friendly they would be for a swap, but they're cute.
Pancake turner spatulas for 88 cents
Dice, 10 pack (in the dollar spot section)