Depends how the studio is set up.

However a crude mix burnt to CD as an mp3 or a wav file should not take very long. Some studios still use DAT for the final mix, so having a couple of spare DAT tapes kicking around is a good idea.

When Im doing a project for people I like, I encourage then to bring an empty big HDD to the last session and I copy everything over for them. Than said most of my friends wont part with tracking data until the bill is settled. This is good for me as it frees up disk space for another project and I am no longer responsible for there data ! It is god for the bad as they can get stuff remixed any time they want !

Other helpful stuff...

know you tracks inside out

keep an open mind

have an idea about how you want stuff to sound but remember to be be flexible

lose any and all attitude, if you upset studio staff they will not try there hardest for you.

turn up sober

make sure you have spare strings, your ams etc all work

and have fun mate, sounds like it should be a blast !