A stronger, revised, articles of the confederation.
How? Sure, they could get a couple of amendments passed, but the AoC required UNANIMOUS consent to amendments, and any significant strengthening of them would be shot down by someone. Probably Rhode Island.
There was nothing keeping a state from declaring independence on their own other than fear of neighbors. My guess is you'd see state vs state war at some point.
One reason: western territorial claims.
ITTL the Constitution doesn't happen, and given the precarious nature of individual states, they might fight to defend territorial claims.
Such wars would be pretty low-casualty though.