Green’s Dictionary of Slang

(US) a hasty cold meal.

1835		G. Kent Modern Flash Dict. 5: Bever – an afternoon’s luncheon.
1846		Swell’s Night Guide 111/1: Bever, an afternoon’s luncheon.
1881		Trumble Sl. Dict. (1890) 8: Bever. An afternoon lunch; a cold meal eaten in a hurry.
[1940		M. Marples Public School Slang 12: bevers [...] light refreshment consisting of bread and cheese with beer was served at what is now tea-time].