I'm just curious to see how other players keep track of their model's Activation and Momentum stats? 

I really enjoy streamlined skirmish rule sets, but wish there was a solution for stat tracking as elegant as the rules themselves. I guess the main ways are the use of a pencil+paper stat sheet or placing dice/tokens next to the models on the battlefield. I like pencil+paper stat sheets as they don't clutter up the batlefield but they also make it harder for players to read the state of individual characters in play without having to constantly ask. 

I've started playing more with paper minis to experience a wider range of games without having to spend time painting the appropriate minis. They also have the added bonus that they can be quickly drawn on to track things like wounds.