In retrospect

Things I wish I knew / had done... no claim to how correct they are.
1. Set up some guidelines with your friends before the first party (or sooner rather than later), to keep each other in check and make sure no one accidentally strays past their comfort zone.
If your friend / whoever is in an altered state of consciousness and has wandered off to a sketchy place, it doesn't matter wtf other "more experienced" upperclassmen say, or if you haven't set up guidelines with them, or you don't know the place they're at. They can always get their fix at another party--it's better to err on the safe side. Especially if she's the only girl in a roomful of guys, more likely than not something is wrong. Discretely talk to someone--try girls over guys--don't give up until you get someone who'll go and just check up on her with you.

Don't be afraid to watch over your friend / limit their consumption / whatever for fear of looking uncool / lame. More likely than not, they won't remember anything, let alone whether you were lame or not.

Exploring Tips

Wear pants you don't mind ripping / wear jeans
Bring band-aids unless you don't mind open wounds
If possible, have everything attachable so that you don't have to worry about carrying stuff or having stuff fall out of your pockets.
Make sure your batteries are charged, or bring spares / a spare light source
Bring your ID
Plastic bags are a good idea for rain...especially if you have a paper wallet...
If you set your cellphone to silent / vibrate, make sure to _un_silence it if you're depending on it as an alarm clock...
Explore stuff...but try not to screw up some poor grad student's experiments
Have fun :) [ Updates 11/6/09 ] Those zippered pouches that can be attached to keyrights / carabiners are really good.
Alcohol wipes are nice too
Trick: Wrap some duct tape around a card to store it compactly (or take a small roll and crush it)
Bandanas are nice, or makeshift a dust mask, e.g. some elastic string (from an ID badge thing at a competition) plus any bit of breathable cloth
Lights with switches and not pushbuttons are nice (esp. w/o headlamp)
Learn how to sew and patch pants
IDs, don't lose them, they can be annoying to search for / retrieve. Tape them down or something.
Those sharpies with keyring caps... they don't stand up to abuse. The keyring part falls off the sharpie too easily.
Socks with holes cut out = gloves
Consider that carrying out a irregular knock takes much more time than straight knocking
Try a sacrifical jacket to minimize skin cuts and protect the hands