Your wallet can be real pain for your back and the buttocks, and it can even lead to shooting pains down the legs. Sitting on a wallet for prolonged hours every day can compress sciatic nerve which passes beneath piriformis muscle and leads to piriformis syndrome, low back pain & self-inflicted sciatica.
The wallet acts as a wedge that forces the pelvis, spine and body out of alignment. Just as you would not sit on a brief case or a rock for an extended period of time, you should not sit on your wallet. Anyone who drives more than a half hour sitting on a wallet, is a candidate for sciatica or back pain.