The current phase of the Moon is slightly important in a werewolf game, how do you keep track of it in your game? this seems more problematic for me because I mostly haven't cared much about how much time has passed overall.
In the past, I used one of several methods for moon phases. I've almost always tracked time in play, at least to the day.
Method 1: Tide Table Books
I would pick up (usually for free) leftover out of date tide table booklets picked up at the end of fishing season. I then used that, despite being the wrong year, as the "official" tide and moon phases for that game.
I used this in my VTM games.
Method 2: Randomize.
I used a d8 to pick which phase it was in.
1: New (3 day)
2: Waxing crescent (4 day)
3: Waxing quarter (4 day)
4: Waxing gibbous (4 day)
5: Full (3 day)
6: Waning gibbous (4 day)
7: Waning quarter (4 Day)
8: Waning crescent (4 day)
I then rolled for day within each, using a d3 or d4 as appropriate. Note that this is actually just under half a day long. To correct that, on odd moons of the year, knock a day out of the new moon (for only 2 such days); on even moons, leave it at 3 days.
Note that this is a 30 day cycle. One can also use a d30.
01-03: New (3 day) 04-07: Waxing crescent (4 day)
08-11: Waxing quarter (4 day)
12-15: Waxing gibbous (4 day)
16-18: Full (3 day)
19-22: Waning gibbous (4 day)
23-26: Waning quarter (4 Day)
27-30: Waning crescent (4 day)
Method 3: Let the players pick at the start of the adventure
Sometimes, I'd just have players agree to what the lunar phase was. Then I went into the adventure.
Note that this was something I did running Dragonlance, so there were 3 moons to track... and I just advanced from there. I used a chart from the DragonLance Adventures hardback, and it was 20+ years ago...
One solution we used was to pick the date our campaign was set in and use a moon phase website (e.g., stardate.org) to keep track of what the phase was for any given day. As time passed in game, we could just look up the phase when we needed it.
This is probably not suitable for the setting you play in, but for those who start a new campaign and make their setting for scratch, or play in a setting where this is possible (I'm sure the question title will attract some of them): make your calendar lunar based. That's what I do in my campaign: I take account of the date, it's not so difficult (how many days each session took and how much time passed between sessions; I have some notes for that). Originaly it was just a handy detail that new month = new moon, but soon the party got a werewolf henchman and it became important. Then two werewolf PCs joined the game and I'm extremely glad for this system.
I GM'ed a game of Scion and one of the PCs had the power to watch a scene from aerial perspective IF the moon already rose. So I searched the web and finally found
The only thing you have to do is keep track of the date.