[Jet Pack Pyro]

Here's a tip for leaving your base, which is often one of the harder parts of being a spy.
Walk up to your battlements as a friendly (most preferably some who can die in one hit from a sniper, like a demo), stand on the ledge and loud cloak while tossing an ammo pack over the ledge, and quickly hop down (after a loud cloak, you can fall for a short period of time without losing your cloak), sneak into the enemy base, sabotage some Sentries, gas nade the spawn, whatever you want.