If you keep your gadgets and gear in a canvas bag or backpack, they won't be very safe if you're caught in a sudden rain storm. You can prepare for this emergency ahead of time by keeping a plastic garbage bag tucked away at the bottom of your bag.
A folded-up garbage bag barely takes up any space, so there's no downside to keeping one handy. If it starts to rain, but you still need to walk a few blocks to your destination, you can open it up (get under cover first if possible) and pull it over your laptops, tablets, and ereaders in mere seconds to act as a makeshift poncho. This tip only requires a little foresight, and even if it doesn't pay off for years, when the time comes to use that bag, it can save you from a major headache.