There comes a time where your baby will outgrow his one-pieces and you'll have to go out and buy new ones. If you happen to have one that you don't want to save (I save most of whats in decent shape for the next little one some day), then you could repurpose it so that you can keep using it for a little while.
You start with a bodysuit. This happens to NOT be the one that I am cutting up.
Then, you want to cut a straight line right above where then leg area is. Here's an example.
The reason that I am cutting up this bodysuit is because one of the snaps came off and I don't really care to repair it. You can see the top left one is missing.
There you have it! Its a super easy, quick 2 minute idea you can use to make your little one a t-shirt one of a bodysuit. I use this as one of the extra shirts in my diaper bag. Its nothing fancy, but it does the job.