How can we use multiple Carcassonne expansions without the game taking forever?
The simplest way is to simply shuffle up the tiles, then pull about 60-150 of them for use. This will typically mean a 1-3 hour game, depending upon player speed and exact number of tiles. It also limits the needed table space. It does, however, also mean it is possible to not have any tiles turn up from a given expansion.

Also, don't use the River nor River II, nor the Count. The River I &amp; 2 simply lengthen setup and increase think-time needed at start.... in addition to taking time to start, and adding 10+ tiles each. The count, by allowing reinforcement as it does, really adds to tactical think-times.

If using princess and dragon, you may want to hold out one volcano, and shuffle it into the play stack after generating the ones you're going to play with. This way, you know the dragon WILL show up, but might not be showing up twice. Same for Tower tiles from The Tower.