After six months with Alpinestars' Orbit 35, I discovered this waterproof expandable backpack is versatile and comfortable.
The roll-top closure works perfectly at keeping the main compartment dry and when used in conjunction with the compression straps has the benefit of allowing you to reduce the size of the backpack when you’re not carrying as much.
The shoulder straps can be adjusted for the perfect fit, and there’s also a chest and waist strap.
There’s a built-in laptop protector as well as a helmet carrier and provision for a hydration pack (sold separately). The only downsides are that it’s pretty fiddly to use and quite pricey.