Searching for the one

Fellow bag heads,

I'm searching for the illusive 'one bag for all'. The mythical 'can do it all'. I basically live in a van with super limited space and need to get a bag that can fit all my use cases.

Use case:
I'll be using the bag for hiking, multi day hikes (summer gear) but the majority of my gear is lightweight so could get away with 38/40L (potentially).

I'm into bike packing, so will be strapping the bag to a rear rack on my bike. The bike packing trips will also include some pack rafting, so potential bonus points for a waterproof bag.

I basically need a bag that is spacious and comfortable for multiday hikes, that is resistant enough and easily strapped to the back of a bike and is potentially waterproof so I don't have to empty the content when on the raft.

I'm not asking for much.

My rational at the moment is either:
A waterproof roll top that won't be the most comfortable when hiking i.e exped.

A proper hiking pack like a Osprey exos 38 with a waterproof liner inside (durable option)

Or do I go for a UL bag that can pack away pretty easy and store it in the TiZip, saving some weight at the same time.

I'm also wondering if a 38L will even store all my camping gear, so do I go for something like this Sierra Designs bag? Although it might be a struggle to fit this on the rack.

https://sierradesigns.com/flex-capacitor-40-60/

I think I've essentially got decision paralysis as there are so many options and set ups and would love to hear what you guys think.

Cheers