-- Relevant to topic \/
If your birthday was after Nov. 19, I'd say have a WII~II party, but since it isn't.. Hmm... I'd say try to come to a basic point on what everyone would like in regards to events, then go with it. Don't get too detailed (obviously won't be able to, due to limited funds), but keep things interesting.
As for food, I'd say (again) see what everyone enjoys.. or you could be variant and maybe get a lot of little pieces of different types of foods, not all junk food. Even when I go to outings, I don't just try to eat my share of burnt marshmellows but also a bit of solid food (i.e. chili, stew, anything that has some sort of real nutritional value to it).
For my 18th, I ended up being out of town.. and so far, every year since, I've not had the b-day song performed for me (thankfully). Of course, even though I was out of town, I was with my family, and we ended up going out to eat that evening. They forgot it was my birthday (hurray!) until after dinner, so no singing at the restaurant for me.. but I got a free meal out of it!
-- Not relevant to topic yet just.. well, got home from work and in an odd mood \/
By the way.. if you're able to Rufus, start saving up for your 21st birthday, so you can actually have a memorable one - not one you end up getting a hangover from on the next day. For example... do what I did for my 21st and go to another country (I went to Japan for mine!). I had to save up about $5,000 (but I came back with ~$1,700 leftover, due to my penny-pinching ways), but it was DEFINITELY worth it.
On a similar note... SE in Japan is rude.. they don't even give tours of their "building" or are friendly at all.. which is actually about three floors in a business tower. And Sony is actually VERY friendly, with a 10-floor showroom and some of the big shots greeting people at the door when they open up in the morning. Weird, huh?