You can always improvise weights - like finding a couple of cans/bags of food or pieces of wood or metal to lift.
Also doing what I think are called 'body resistance' exercises where you use your own body weight with no extra equipment needed.
Here is a website where you can choose a particular muscle group you want to work on and see what workouts can be helpful
http://www.exercisedb.com/exercisedatabase/exercise.asp