Start with three: G, C and D. In the key of G those are the 1, 4 and 5, and they carry most bluegrass, old-time and folk tunes. Add Em for the 6m and you've got a big share of country and worship songs too.
0 0 0 02 0 1 20 2 3 42 2 2 22 1 0 23 2 1 33 3 3 32 0 0 22 2 1 24 4 3 40 2 3 34 2 2 4About that 5th string: it's a high G drone, so it sounds great on G, C, Em and D, and a little tense on A, E and F. Lots of players let it ring anyway, or leave it out of the roll on those chords. When you capo the long strings for a new key, slip the 5th string under a railroad spike at the matching fret so it moves up too.
Bluegrass bands love A and B. Rather than learn new shapes, most banjo players capo and keep their G-key shapes. The capo chart shows where, and the transpose chart does the rest.
Chartless listens to whatever is playing and shows the chords live. Pick banjo as the instrument and each chord comes up as an open G banjo shape, and the tuner has banjo open G and double C targets. The live chart is free.
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