It can be a challenge (especially in this economy) to find cool things for the grab bag. But her are a few places you can check out.
Best Buy has a whole section of under $10 items
Five Below has 27 stores in Massachusetts
Non-perishable food items at your grocery store can work well
You can filter amazon for under $5
Ocean State Job Lots has about 100 stores in Massachusetts
Of course you can check out all the stores like Walmart, Dollar store chains, and the rest too.