It's up to you but there are other things you can use. I have used gallon milk containers filled (or partially filled with water) for some weight when I had nothing to work on.

Also there are weight bearing exercises that are free like push ups and squats.

Lately i've been doing water aerobics twice a week and walking my two (over 40lb) dogs twice a week - one mile and pulling two doggys in is plenty good weight training. My arms are pretty solid... too big still but SOLID.

Then there are alway free power walks, jogs.

Motto: No matter how -- just sweat every day!