MIT is developing proverbial wallets that physically change as your electronic accounts grow and shrink. They aim at "unabstracting virtual assets" - just as the amount of bills and coins in your pocket unabstracts how much physical money you have.
I particularly like the "Mother Bear" model. It has a hinge inside, and an electronic connection to your bank. If making your monthly budget goal looks tight, the wallet makes itself harder to open. That is a good nudge.