Eating or drinking, if you're riding in a pack or paceline, it's almost always safer to do it at the back end of the line. That way, if you inadvertently veer, you're less likely to take somebody else out.

As for eating, if you can, pre-open whatever kind of package your food is in before you start out. (Tearing open a wrapper can be pretty challenging when trying to maintain pace.) Then, take smaller than usual bites, space them out a bit, and rinse each bite or two down before going for the next one.