Daniel Coyle who wrote The Talent Code had an interesting blog post recently about a kid who wore googles with the bottom half of the lense darkened to help him practice dribbling basketball. He also mentions a couple more simple yet effective homemade devices that people use to increase their skills.
Then I realized that I had a few such "gadgets", mental ones, that I use in memory training. One is the good old automobile license plate--a constant source of random numbers and letters. When I was working on my Day of the Week technique I used to consider that the first number and the last two on plates were month and days and quickly figure out the DOW before the car disappeared. Since I walk a lot, it created many opportunities. Now that I'm working on speed number memorization I'm back to using the license plate. I take four numbers from it and create two images on top of the car. It's a good way to make your brain work a little faster and under some pressure.
And Josh mentioned that he used Google Search as a tool. Several people use a metronome.
Do you have a mental "gadget" or technique that you use?