Okay, okay, first calm down, and DO NOT have it this weekend! This Saturday morning go to several on your own. Just ask how much different things cost. Bring $5, at most, just in case something fun comes up.
Then, go to $1 store and purchase one of those packs that let you put prices on there.
Start at one price. If you see that people are shocked by the prices, make a sign that says "Half Price".
I'll give you some ideas, though: shirts that you can tell are worn: $1. Good, brand name ones: $3. Used water bottles: $1 for the better kind (like, if it has a tube in the middle that you can freeze); otherwise, 50 cents. Stuffed animals do not do well; everybody's looking to unload them. You might get lucky at $1.
You can probably get $100 for the day bed, IF you put an ad in at Craigs List, letting people know. (Otherwise, your average yard sale goer will not be looking for a day bed.) Side tables -- honestly, I'd have to see them. I would be comparing them to the prices at consignment and thrift stores, depending on quality. Headbands and clips -- $1-$2, depending. "LIKE NEW" clothes = you can probably get $5-$10, depending. (Oh, I just realized you were thinking the same - ha! GMTA!)
I don't want to sound like a downer; I'm a realist, and I've been to many consignment stores, thrift stores, and yard sales. If you price the same as thrift stores, you'll get their attention; yard sale prices are typically a bit smaller, but you don't want to come across desperate, either. No matter how cheap you go, many people will try to barter with you, which is why you want to go higher at first, because you can expect that to go with it, anyway.
I really hope this helps.