All you need is a pair of shoes (laced), an inner tube, and scissors. Go to your local bike shop and ask for old inner tubes. Explain why you need them and they will most likely always give them to you.
Step 1: Unlace shoes
A very easy part. Take off the shoes' old laces. Keep them around to get a sense of how long the new ones need to be.
Step 2: Cut inner tube
(You can use scissors, x-acto knives, or rotary cutters to cut it)