I'd recommend you bring a notepad, a few pencils and maybe your laptop if you have one (just to transfer files if necessary). I suspect this kind of private, primary meeting will be pretty low-key. I've met new PSMs over drinks at a bar, in the middle of huge production meetings, and even on first rehearsal. The chance to get together before rehearsals begin is a good thing - this is a chance to get to know each other, to know the PSMs expectations and needs, find out a little about the productions and its specific challenges, and where you fit into all of it.
In the professional world, ASMs may or may not be a part of pre-production work, depending on the contract requirements, the size of the show, the producer, etc. Production contracts (Broadway), for example, require the PSM gets 2 weeks paid pre-pro, 1st ASM gets one week of paid pre-pro and the 2nd ASM gets at least one day prior to 1st rehearsal. Some regional theatres I've worked for default to give ASMs 3 days or more of paid pre-pro depending on the scale of the show. As a professional ASM, I prefer to do pre-pro work whenever it is possible. Helps me get to know the show, the company, etc, which in turn makes me feel more confident heading into first rehearsal.
But the scope of work during pre-pro varies by show and PSM. I've spent days of pre-pro with tasks as varied as setting up a rehearsal hall or temporary office, pulling rehearsal props, communicating with department heads about scheduling, chained to my computer editing reams of paperwork or prepping actor packets. Only your PSM can tell you what your tasks will be - so go into the meeting prepared to listen and take notes and you should be fine.
One word to the wise - dress neatly (first impressions count, after all) but still functionally. My first day at my first internship I dressed very nicely since its was an SM-only kind of day and I ended up hauling lumber in ballet flats by 5p. And the PSM commented on my shoe choice. Lesson learned.
Good luck!