Green’s Dictionary of Slang

few, a n.

1. (a good) many; a great deal.

2. [mid-19C] someone extreme in manner.

3. [late 19C+] a number, unspecified, of drinks; usu. as have a few

4. [1900s–50s] (US prison) a short prison sentence.

5. [2000s] a short time, i.e. a few minutes.

In phrases

put a few back (v.) (also put a few down)

[20C+] to have a few drinks.