You don’t plan to get luggage wet, but it happens. Some luggage will be treated to be waterproof, or at least shower-proof. If you are camping or hiking it may be useful to make sure that there is waterproofing.
5. Opens and closes
Nothing is more frustrating then fumbling around trying to open or close your luggage if it does not do so easily and quickly. The best is zippers, both because they can be quick, take a lot of strain (modern ones anyway), plus they can be easier to repair if they do break.
Being able to lock your suitcase is useful and often important. Some luggage come with padlocks already, or you will need to purchase a lock separately.
If you do purchase a lock separately, check it will fit your luggage and that it actually locks. Consider whether you would be better getting a key or combination lock – are you the type of person who loses keys or forgets combination numbers?