Robar'd and folding stocked and scoped Glock 20 with .224 Boz, 40 S&W, and .22lr conversion kits on hand. Also, suitable suppressors, a few dozen 30 round magazines in addition to some flush fit ones, and at least a few thousand rounds of HP and steel core AP ammo, and about 10,000 rounds for the .22. Full auto capabilities would be cool, but probably not very useful.
Granted this is unrealistic, but it would be a configuration that would solve most problems that could be encountered.