As others have said, you get used to it. If it's allowed, chewing gum might be a good idea. Just don't let it fall out of your mouth into a body cavity... haha. Oh and wear clothes that you ONLY wear to lab- like scrubs, and wash them in hot water after lab.
Do eat beforehand, maybe not a huge lunch if you get queasy, but you need some protein to stick with you until you're finished dissecting- this should help prevent any lightheadedness too. Just remember, if you start feeling faint, please find somewhere to sit. You don't want to pass out and cut your head open on the tank, or cut yourself with a scalpel.
What IS it about anatomy lab that makes you hungry?? It's right after lunch for us and I'm always starving about an hour in.