As for a sealed case, you may have seen ads for Pelican Cases, which are fully gasketed, and made from thick, impact resistant plastic. These are seriously rugged, and a great way to protect fragile equipment of all kinds. Pelican makes a model designed specifically for laptops, which I’ve seen cruisers dutifully toting to internet cafes. There are even large models, including roll-around ones with handles, which could hold a whole mobile-office worth of equipment.

Other options worth considering are kayak/rafting dry-bags or waterproof backpacks. If you already have a laptop case you are happy with for carrying all your goodies, sealing the whole thing up in a dry-bag would be nearly as effective as a Pelican Case. And waterproof backpacks (which use dry-bag-type construction) are useful for ferrying all kinds of water-sensitive items ashore as well as around town.