A cheap micrometer, and some simple hand tools for working with metals, plastics, etc. Files, screwdrivers, rulers, etc. An Arduino starter kit with plenty of

A cheap micrometer, and some simple hand tools for working with metals, plastics, etc. Files, screwdrivers, rulers, etc. An Arduino starter kit with plenty of servos, sensors, etc. All run off a few batteries, and relatively safe. It's amazing what kind of instrumentation you can get for less than $100 these days.