To clean cotton canvas simply use soap and water. Allow to dry naturally. Do not machine wash.
As with life, your brass fittings will mellow and age with use. You can clean them with a good quality brass cleaner should you wish to.
Leather will harden over time so in order to maintain its patina and keep it supple it should be occasionally rubbed with good quality leather cream.
We get nearly 40 inches of rain a year in Carlisle...
...Which is why we make our bags with British weatherproof bonded cotton, which means it'll stand up to being caught in the rain.
Even we wouldn't take it swimming though!