There are two things I always carry when I travel with a baby: a couple of flat cloth diapers, and a bottle of simethicone drops (aka Mylicon)
The diapers are hugely useful. They are soft and absorbent, so they are great for mopping up all types of spills, or drying off if you get caught in rain. They dry quickly, so if you wash them out at your hotel, they will be dry again in the morning. You can even use them to drape over the stroller hood to block the sun from a sleeping child.
Sometimes local water can differ a bit from that at home, even if you are using bottled water. Travel (especially air travel) can disturb digestion a bit, as can changes in feeding schedules. Simethicone is priceless to have around if a baby develops a bad case of gas. Even babies who are exclusively breastfed may need it at times.