I second (5th?) a lot of the suggestions you've received. I've been perfectly fine taking one full 3 mm wetsuit, but some people have needed a skin/sharkskin underneath or a 5mm full wetsuit, plus a beanie. It totally depends on your tolerance.
At least 4 swimsuits come in handy. I find that by the time the night dive comes around, you might not want to get into an already wet swimsuit. So, 2 swimsuits one day, rinse and hang to dry. Men's swim trunks might dry faster, but I find I prefer another swimsuit the next day. Ok, maybe it's a fashion statement.
I always wear my neoprene socks, but people love lycra socks now.
My spring loaded clips were from Canadian Tire, but I'm sure you can get them from Home Depot or a hardware store or get the Nemo or other character ones even from a dollar store.
A light dollar store over the door shoe organizer came in really handy on the Belize Aggressor III for little things like sunglasses, moisture muncher packs for the camera housing, watch, shoes, etc.
I take a sleeve of various just-in-case over-the-counter meds such as Sudafed, Buckley's Cough and Cold, Gravol, Immodium, Reactine, plus DomeBoro Otic or Star Otic (Dry ear drops), Polysporin ear/eye drops, Polysporin or other antibiotic cream, plus various bandaids.
Aggressor has all charging done at a charging station on the dive deck, so have all of your items and cables labeled. My combination travel surge protector with outlets and usb ports was very popular.
For traveling abroad, a lot of countries don't have grounded outlets, which puts your electronics at risk, so I carry 2 small grounded single outlet converters. Cheap insurance.
You might want to check if you need a Hi-Lo converter and any adapter plugs in your hotel.
I started a similar thread last year in the Aggressor forum if you'd like to take a look:
Tips for the Belize Aggressor III?