WHAT TO RIDE
You don’t necessarily need a new bike. A mountain bike, hybrid, gravel bike or tourer will do the job. Wider tyres will allow you to ride more comfortably over rough terrain and knobbly ones offer extra grip in mud. Lightweight is also helpful, especially as you’ll be loading it up with extra kit and may need to lift it over obstacles like trees or stiles. On the subject of loading, as previously mentioned you’ll want space for bags at the frame, handlebars and under the saddle.
Ensure you’ve got a riding position that will be comfortable after several hours. You could consider a few extra tweaks like replacing the saddle.