I have learned to ask for a refill. Rarely is one offered. If the flight is reasonable length (over 75 min), I generally get a refill of alcohol or non alcohol w/o problem in C+. Often, your best bet, is to ask the FA coming from F to C+ to do the first trash run for the refill. In my experience, about 50% of the time they will finish the trash run then bring you the refill. Also, if the carts came from the front galley and the flight is longer, ask for the refill as the FAs are on the way back up. But I have become willing to make the request via the call button.