Depending on the nature of your trip, you may want to consider several options:
*If you’re travelling mainly by boat with little to no hiking, you may consider getting a large dry bag for all of your supplies. These are extremely sturdy and generally do a good job keeping things dry, if mice don’t eat holes in them. However, I’ve had to portage these across rivers, through the jungle and along beaches, they aren’t the funnest thing to carry for long distances.
*If you’re travelling primarily on foot, I would suggest a more traditional frame pack such as used in back packing with a water proof covering, you can also line your pack with heavy duty trash compactor bags or light weight dry bags to keep everything inside dry.
*Another thing to consider is bringing a smaller day bag for day hikes or other smaller side excursions. This can be almost anything, as long as it’s comfortable to wear for hours of walking and can hold everything you need inside.