Dollar Tree Birthday Deals and Deals NOT Worth the Money

My youngest is turning two in August and I have been starting to think about what to do for his birthday now since I have a lot of upcoming events and don't want to rush into crappy decisions with shitty, not so well thought out decorations. I'm thinking I want to do a space theme. When I start looking for birthday stuff, I always start at the Dollar Tree because they have a pretty decent selection that you can piece together for cheap.