ThinkGeek already sells a wearable sound effects device, but if all you want is to stomp like a mecha check out the shop’s very own Giant Robot Slippers. They emit the appropriate sound effects when you raise and lower your feet.
Fortunately, you don’t need a nuclear reactor to power the slippers. Four AA batteries will do. They also have a power switch, which naturally should always be on the “On” position. Otherwise what’s the point?
Summon the browserzord and buy the Giant Robot Slippers from ThinkGeek for $30(USD).