Whenever I build a new bike or get a new saddle or seatpost, for the first handful of rides I get all Eddy Merckx on that shit. Sliding it around on the rails (although they invariable end up pushed all the way back) and adjusting the tilt. For those situations I keep this combination 5-6 hex wrench in my tool kit (always) and my pocket (sometimes). It's really good for getting at saddles when you also have a seatpost mounted light, and is also handy for stems, especially if you've got that thing going where your top cap is a 5 and your stem bolts are sixes (this also pertains to seatclamps and seatposts).
The tool is made by Lifu and is a "N" wrench 5/6. This particular one was given out by Surly as a tradeshow giveaway a few years back and is one of my prized possessions. The standard Lifu ones can be picked up for around $4, although I'm not sure if they're currently in manufacture. If any of you bother to find out if you can still get these anywhere, please do let me know as I'm looking for a backup.