What George actually says is this:
"Me an' Lennie's rollin' up a stake... I might go an' set and have a shot, but I ain't puttin' out no two and a half."
The reader can infer several things from this comment. First of all, this makes us believe that George sees putting out money to be with a girl as wasteful. Secondly, we see that George has a higher purpose that he believes in. Many of these guys are only living in the moment. They make their money in one week and go blow it the next week. Not George, his plan is to work together with Lennie and get their own little ranch. This shows frugality on George's part. It is a strong character trait. So, having a drink, that doesn't really cost much and it was a nice way to reward a week's work, but to spend money on the chance to be with a woman would be frivolous.