I've never had a problem using expired vouchers. I also don't drink much and rarely use them on myself. The odds of me being in coach and wanting a drink aren't that high. I generally use them on people who appear worthy - if I see someone swap their seat to help someone else, for example. Or if there's a lengthy delay or other frustration, I'll give the FA a whole bunch and ask him or her to dole them out to the needy/desirous. Simple way to spread some cheer. And there's a lot of travelers out there who need that cheer!

I'm reminded of a "battle" I had several years ago when cash still ruled and I had none. I wanted to buy a snack box, the guy next to me wanted a beer. Both were $5. I had a drink chit worth $5 which I said I'd use for his beer, and he had a $5 note which he said he'd use for my snack box. The FA simply wouldn't have any of it, until (with appropriate dramatic effect as we were both rather amused) he handed me the $5 note, and I handed him the drink chit, and then we both handed them over to the FA.