Thanks for the suggestions. I know I'm going to totally overpack for this which is why I'm trying to figure things out now. I think it would be much easier if I was staying on AC the whole trip, but I'm planning on spending a few days in San Ignacio and was thinking of taking the bus to get there (not nearly as easy as throwing the suitcase in the trunk). Then, to complicate things more, I've also been thinking of spending a night in/around Flores instead of taking a trip to Tikal from SI... That's a lot of lugging on a lot of public transportation so less is definitely going to be better.
How does one pack for visiting such different area? The beach I've got figured out... shorts, check, t-shirts, check, bathing suit, check. But for evenings and days spent in/around the jungle exploring ruins, etc... How cool does it get in the evenings in October?