If you could only use one pedal...

Richardj

Hardwire Supernatural.  You don't need reverb built in although it can be handy. Most amps can get a decent (ish) drive tone.  However, with the scope of ambient tones and scarily accurate spring and plate modes available this little black box deserves a place in in the pedal hall of greatness.

noisepolluter

Assuming the amp is a deluxe reverb, and the reverb/trem footswitch doesn't count...

probably the Liquid Sunshine for drive, or the deluxe memory man for delay/general wibbly noises