Same thing happened when daughter2411 borrowed my favorite suitcase.

All suggestions will diminish the odor. The key word is diminish - not to be confused with "rid."

You may think the smell is gone, but humidity will magically reactivate the telltale odor. Luggage doesn't have to get wet.

I had more success getting rid of the smell of death than cat pee smell. Don't get excited, the death smell happened when daughter2411 turned off the freezer in mid summer when she was 4 yrs old - wasn't noticed until the lid popped open. Oh my. (why don't we have a 'stinky' smilie?) She got her pay back 10 years later. Her cat wet in her leather shoe. Thinking she had gotten rid of the smell, she wore the shoes. Yep, body heat will also reactivate the odor.

I second the suggestions UAL_Rulez listed.

How to keep cat away from luggage:
1. Put luggage away / out of cat's 'space' between trips.
If no area off limits to cat:
2. Sit bag up, (less area to lay) & put lemon extract on cotton balls, place inside mesh bag & hang from handle. Lemon extract is a natural cat 'go away' tool. Don't over do or you will smell like a lemon tree on your next trip.
3. Cats also shy away from cedar balls & moth balls. Don't use moth balls - explanation probabaly not needed.
4. Don't wash luggage with anything with ammonia in it - ammonia draws cats & tells them to "please pee here"
5. Don't use 'cat go away' spray inside luggage - clothing will absorb that odor.