Dollar Tree is a great place to go to get products that are traditionally overpriced. You friend doesn't care that you spent $6 on her gift bag for her present--so why not spend $1? Sending thank you cards after special occasions can also get costly, which is why I choose to get an 8-pack of cards for $1 instead of $4-5 at the local greeting card store.
The store is always clean and the staff is very helpful finding products. Just don't bring your debit card because they are a cash-only business.