It depends on where you are going (is it a cold destination or hot?) and how long your stay will be. Assuming that it is a 7-10 day cruise, I would suggest at least 3-4 pair of shoes. I highly recommend flip flops for pool areas, your comment regarding 1 pair of shoes for formal night is good, then you want at least two good shoes for wallking: a pair of tennis shoes and the teva's are a good. If you don't take your teva sandals, I would suggest a shoe such as the easy spirti walking shoe. Hope this helps.