I’ve never liked the idea of bucket lists. If swimming with dolphins is that good, then do it as often as you can, not just once so you can post the pictures on Facebook.
Anyway, never mind the mini rant;
What do you want to do on a bike, haven’t done yet, but have some plans, no matter how vague, to do in the future ?
Could be anything that needs time, commitment, training or all three.
1. For me, it’s ride the Stourport Ring and Avon Ring, two local canal loops of 74 and 107 miles.
2. Do some proper bikepacking/bivvying, either solo or on the tandem.
3. Ride every bridleway within 10km of home at least once. Then extend to 15km, 20km, etc.
Once I’m comfortable with number 2, I can then move on to;
4. Ride the Mercian Way, 230 miles of Sustrans Route 45.
5. Cross every possible bridge over the River Severn by bike on one journey.
5. Ride up the Severn Way from home to the Hafren Forest, back down the Wye Valley Walk, then back up the Severn to home again. About 350 miles in total.