After using a bath towel, hang it up to dry and re-use it the next time you shower/bathe.
This is one of those simple, money-saving tips that I thought everyone did - until I started talking to people about it. I have friends who never thought to do something like this, so I thought I should share it here. This tip is especially helpful if you have children. If we didn't re-use our towels once or twice, I would be doing laundry all the time.