Ortlieb are the brand of choice for serious bicycle tourers. We use rear panniers and take the waterproof sacks. These are light, sit on the bike rack and can accommodate varying volumes of food and bad weather gear. We attach them to the rack with flat elastic straps.

We take a couple of the ordinary round, more springy, straps as well to fasten the bike to rails on trains and ferries.

The Ortlieb handlebar bag is good for carrying valuables and has a waterproof map case that sits on top; this is either completely non-ergonomic or I've missed the point of how to use it; but otherwise the bag is useful.