Essential Gear

My essentials list

My gear will vary slightly depending if it's a single- or multi-day trip or there's any planned off-roading, but the core gear remains the same.

Water - I use a 2L Geigerrig bladder in a tank mounted Kriega US10 (with some other stuff) so it's handy. I find a backpack reduces airflow through my jacket and I often have a camera hanging around my neck which tangles in the straps and hose.
Designed to be pressurised for a number of benefits and it's really useful to have water on tap around camp too.
If I ever do an extended trip I would consider pairing it with a water filter such as the Sawyer Mini.

Flapjack, nuts and dried fruit, trail mix or GORP, any snack that is calorific and keeps well is welcome aboard. I won't always bother if  I'm sticking to Tarmac or on a shorter ride but it is great to keep you going mile after mile.

Trangia - stable, windproof and nothing to break. Gives me options from just hot water, re-hydrated meals to a fry-up. Just depends on the situation and what I fancy.
I added the Trangia cutting board/straining lid, a stumpy wooden spatula and a collapsible x-mug which all still fit inside. The "optional" drawstring bag keeps any soot residue off of the rest of your gear. Optional on shorter trips.

Tent - large enough for you and your gear. Must handle heavy persistent rain and wind and have good separation of mucky gear and the clean (dry!) sleeping area. I used a North Ridge Torre XL for quite a few years but have switched to a Berghaus Cairgorm 3 (pictured above). It's design is storm resistant and freestanding so it is easily moved about to adjust your pitch or used on rocky ground. I carry a cheap tarp and paracord (when tentless) for any unscheduled stop in foul weather.

3x pairs of socks and underwear - working on the principle of wash one, wear one, spare one. Quick drying and compact types allow easy laundry cycling. I have a line strung up inside my tent to aid drying. Wash them at the same time you wash yourself (however that may be).

Tools (I still need to work on slimming these down).

Mini compressor - my old stripped-down mini compressor finally died and the cheapie replacement wasn't up to the job. My buddy has a small one and it seemed it might fit under my seat (not much room at all under there). So I bought one; a MotoPumps Air Shot. Not cheap but worth it. I managed to repackage my Stop 'n' Go puncture repair kit into the same case and still fit it under my seat!

Sit/kneel pad - I made mine from thick closed-cell foam that I rescued from a bin and use it all the time on the ground or on top of my panniers. Saves my knees, stops wet/muddy socks when pulling on bike trousers and folds in half to keep muddy side contained and off of everything else. Rarely take my Helinox clone unless I know I'm going to spend a lot of time sitting around.

Mini shovel - clearing mud and sand, digging a drainage/run-off gully at camp, can be used as a hatchet to clear brambles or even a ground anchor for the MRS (see below) if needed and done right.

Motorcycle Recovery System (MRS) - to stand a chance of righting a big bike that's somewhere it shouldn't be, I carry a 5:1 Z-Rig system that I put together. I'm much happier to try something more trickier knowing I have this with me. If you always ride with others it's probably not necessary.

Can also be used to drag a fallen tree off the trail.