One thing I wish I had packed was a plastic drain cover.
I am talking about either the flat round plastic piece you use to cover and sized drain or the taller molded pieces that you push into the sink’s drain to keep water in the sink.
Why I recommend packing some sink stoppers for your travel.
Hand washing laundry!
Washing your snorkel gear.
I have noticed that most sinks I have come across in hostels and even the hotels where I stayed in Mexico, lacked the metal water stopper to keep water in the sink.