Green’s Dictionary of Slang

(US, Southern) drunk, thus half-snapped, tipsy.

1838		J.C. Neal Charcoal Sketches (1865) 48: Never go thumping and bumping about the streets, when you are primed and snapped.
1843		W.T. Thompson Major Jones’s Courtship (1872) 93: I like to forgot to tell you about cousin Pete. He got snapt on egnog when he heard of my ingagement.
1848		North-Carolinan (Fayetteville, NC) 18 Nov. 1/6: Drunk [...] primed, slewed, half-slewed, half-snapped.
1851		‘Losing Game of Poker’ in Burke Polly Peablossom’s Wedding 46: Bennett and Smith were both at the grocery, the latter about two-thirds snapped.