Cross-contamination occurs when gluten-free foods come into contact with foods that contain gluten. It can happen during the manufacturing process, for example, if the same equipment is used to make a variety of products. Some food labels include a may contain statement if cross-contamination is likely.
After getting a tattoo, swimming must be avoided until the skin has stopped peeling and all scabs have fallen off. For most people, this means waiting a minimum of two weeks.
If you can bathe while keeping it out of the water (you don't want to keep a new tattoo submersed under water), you can bathe right away. Either way, you definitely want to shower/bathe regularly! I'd never advise anyone to not shower until the scabs went away, that can take a couple of weeks sometimes.