OK, I don't know where you live, but camping in winter is really a sleeping bag proposition if you don't know what you're doing with blankets and such (which I don't).
Most people start with military surplus for a reason: it's cheap and it's durable. Won't be terribly light, though. Recommendations: hit your local surplus store for:
ALICE pack -- a medium should be fine for a weekender, and you don't need the frame for the medium.
First aid kit -- won't be ideal, but most military FAKs have more than you're likely to need. Even close to home, you want a FAK.
Canteens -- you said you have one, get another, and I'd advise having covers, cups and the little stove stands for each.
Sleep: a surplus sleeping bag can be had cheap. The entire MSS would most likely cost more than your entire budget, but you can get the older ICW (Intermediate Cold Weather) bag that predates the MSS for fairly cheap (got mine for $40). You said you have a sleeping pad, so go with that.
Tent: if it's real cold, you'll probably want a tent of some sort. You can get a cheap wal-mart type tent, or go for the surplus pup tent. The pup tents aren't real light, but they are easy to set up and are warm.
Food is easy, just d like others suggested and pack stuff from the house: tea bags, single serve instant coffee, hot chocolate, etc. Some food, SPAm makes a good camp food along with some bread, hardtack, etc. Oatmeal, grits, cream of wheat for breakfast, etc. Hint: if boiling water for a drink, boil in one canteen cup and pour it into the other to make the drink -- keeps you from melting your lips off.
I'd also carry a spare set of clothes, especially socks. If you're only 10 minutes from home, don't worry too much about weight or all that other stuff, just go have fun and note what was useful, write down ideas on what you'd like to try next time, etc (which means bring a notepad and something to write with.)
Hints with the ALICE (if you go with that): Roll up your sleeping pad and strap it to the bottom of the pack. Roll your sleeping bag up in the tent and secure it horizontally across the top of the pack using either the top straps or top flap to hold it in place. Put clothes, FAK, food, etc inside. Canteens can be clipped to the loops on the side of the pack. The outside pockets can hold your fire kit, etc or a 1L water bottle from the store (to not have to worry about filtering water, etc on your first time out.
Maybe pack afield guide or something and try your hand at plant identification, try some woodscraft projects, etc.
Most of all: HAVE FUN!
