EDIT: If you want to go work for a restaurant and a hotel then be my guest, you have answered your own question. You need to go through training so by the time most training is up you have 3 weeks left. Unless you apply now and apply strickly for seasonal it would be too late by the time its winter break. So yes go find a job to apply too its never too early for that. Retail is the worst during the holidays and will not be worth the couple hundred you will be making compared to the stress you will get aside from being a student as it is.

EDIT: You have to really hound at the agencies. They go based off of how much you realllllly want to work and most of them deal with temp to hire situations. you also need a pretty flexible schedule. why not tell them you are looking and by the time its xmas time they will have something lined up for you.