What's the best way to keep sushi fresh for the following day? I like to prepare makizushi in the night so that I can take it in to Uni the following day and have it for lunch. They're made using nori, sushi rice and some vegetables. 

What's the best way to keep this fresh for the following day - I normally box them up the night before ready for the day?
I think the issue is that your nori will get soggy if you make the rolls in advance and store them overnight.  Nigirizushi may be a better bet for making ahead.

Chirashizushi is an older style of sushi which is essentially a bowl of the sushi rice, with the garnishes either mixed in or on top. It should be well amenable to advance preparation.