I think it's useful to learn how to play blend (2-note) chords quietly during jams while other instruments are playing or vocalists are singing -- it will reinforce your understanding of the songs, strengthen your familiarity with keyboard, and ultimately make playing melody much easier.
If you drop your left hand and keep your right-hand fingers in the "home" position (i.e., index finger on the 5 key and your other fingers on the 6, 7, and 8 keys), you can play pretty much all the basic blends you'll need:
In Key of C -
C = any combination of push keys (I usually use 5-6 push = G & C notes)
F = 5-8 pull (= A & F notes)
G = 6-7 pull (= B & D notes)
In Key of G -
C = same as above
G = same as above
D = 5-7 pull (= A & D notes)
Because many G songs don't have a lot of C chords, you may find yourself at times with the bellows fully extended. To avoid this, you can play a G octave (5-8 push) in place of the G blend, which will give you a chance to push instead of pull and get the bellows back where you're comfortable.
In Key of F (rare, but just in case) -
F = same as above
Bb = 7-8 pull (= D & F notes)
C = same as above