Just wanted to see if anyone went to one of these meetings and then wished they had asked something or done something differently.
I've thought of something else I wanted to ask after every type of every meeting I've ever had for my kids! And like you, I also always try to think up every possible question I can before the meeting

Sooo.. my *first* question (if I haven't already asked it) is to be sure to ask what to do if you have more questions after the meeting - can you ask via phone or email, or is it best to schedule a follow-up meeting. And after the meeting, I usually let myself think through the info for 1-2 weeks before following up; in your case I'd probably wait until you have the report in hand for your final follow-up.
The other thing I'd do is to make a list of everything that you're concerned about re your ds and school etc. If you aren't familiar with the type of tests that your ds was given, you could look at a brief summary online that shows descriptions of subtests, skills measured by each etc - but I wouldn't over-obsess about learning everything ahead of time. Your psych will probably go over things in detail, and you'll have chances to ask questions at the appointment.
In general, I've found that I had so many questions during the meeting, and those questions (particularly the first time my kids were tested) usually were very different than what I'd anticipated I might be wondering about... so trying to predict what to ask ahead of time would have been very very tough if not impossible. Definitely ask about the impact of whatever is found at school, and for recommendations on accommodations (you'll probably get all of this without asking). You can ask about school placement too - our neuropsych sees so many children that she's collected quite a bit of knowledge about the different schools in our district over the years, and that's helped us tremendously in determing where to send our children to school.
If therapies (OT etc) are recommended, ask for the psych's recommendation of a good provider. You can also ask your ped too.
Be sure you get some forward-tips, not just "here and now" tips if a disability or challenge of some type is diagnosed. If your ds needs accommodations now, for middle school (?) also be sure you have an idea of what accommodations he might need for high school - you won't know for certain because things change with time and you'll learn more about how things impact him as time goes by and he tries new accommodations, but it's still good to ask for a general idea of how his needs might change as curriculum/courseload etc changes.
Good luck!
polarbear