My group is running a series of published adventures. I am GMing one of the modules (level 21-24) after which another member will be taking the reins.

I have plans for a side-adventure that will take place either before or during the published campaign. It will be a significant undertaking and probably consume enough sessions that the adventurers could gain a full level before they even begin the published content. If I then run the rest of the content as written, the PC's will be a level too high for the next adventure, which puts unwelcome pressure on the new GM.

To alleviate this, I'd like to not reward experience during my side-adventure. But as a player, I know EXP is the most desired reward of all. I considered reducing the experience gained from both the side adventure and the published content so the end result is the same. But the players will surely notice.

So I'm left with one option. Reward the players with something just as desirable as experience points--without unbalancing the game (super-powerful magic items are out).

What can I do?