Gotten stuck in mud or snow before? If you have and realized that (usually) if you let out some of your tires' air, you can get out due to the increased surface. This is what 4x4's will most of the time do if there's no one around to winch them out and there's nothing to attach their winch to.
If you have done this (let air out), then you'd realize how long it usually takes to get down to the psi you want. This is especially no fun in the winter time. Sitting outside in the freezing cold, while cars pass without stopping to ask if you need help, letting the air (slowly) out of your tires to better your chances at getting free.
Well no more shall you have to do this. Now if you follow these instructions, you can easily switch caps and sit in your warm car while your tires deflate (time it around 2 or so minutes, depends on the size you make these and your tires).
These can also be used for "pranks", but I'm not here to say you should use these for such things (although the pictures kind of gives away what I made them for, but never got around to using them).
Step 1: Yellow Peas aren't just meant for eating...
Sorry, no actual pictures cause I made these a long time ago and never took any.
But I did make these instructable guideline photos when I made them and just found them recently.
We'll start out with the fast (both to make and to deflate) way.
Tire valve cap (aka Tire stem cap)
Steps (just as the picture says):
1. Cut yellow pea in half
2. Use super glue on the half pea and push into the bottom of the valve cap
3. Let it dry
4. Switch caps on desired vehicle when needed.