When indecisive about what kind of drink to buy think glass > aluminum > plastic.
Glass is the best of the three.
Always bring your lunch! Why spend money everyday on a meal when you can bring it straight from home! Think of how many styrofoam trays are being thrown out every day just because you were too lazy to pack a lunch the day before.
Walk or ride a bike as many places as possible. Not only do you save money, but you are also staying fit and healthy! No matter how short the distance you drive, the moment you first turn on the engine is when the most toxic fumes are being emitted.
Avoid creating trash wherever possible: when ordering food, avoid receiving any unnecessary plastic utensils, straws, etc. (ask in advance), buy ice cream in a cone instead of a cup, don't accept "free" promotional products, buy products with the least amount of packaging, etc. Every little bit of trash avoided does make a difference!
Bring a mug with you on outtings. You can use it for take out beverages without asking for a disposable "to-go" cup.
Save your food wrappers! Reuse! They make great wrapping paper, all you need is a little tape.