Bikepacking

Rucksacks over the smallest and bikes aren't a happy combination over any osrt of distance.  The more weight you can get off your back the more comfortable it is.  You'll not get much in to a bar bag, and if you do it may upset the steering.

Pete.

I'd agree with Pete, except that I'd ask what sort of route you're thinking of, on or off road? If you intend doing a lot of "rough stuff" then panniers aren't great (possible - I've done it - but not great as they rattle and shake, tend to catch on things, make it hard to pick up the bike if needed, and your rack and pannier fixings need to be strong to take the jolting). But putting the load on your back does mean keeping it very light and compact.

A couple of other things to bear in mind - i) carrying enough basic tools to keep the bike going (pump, spare tube and/or puncture kit, probably tyre levers, some kind of multitool, and a bit of lube, should cover most "routine" problems); ii) keeping the bike secure, carrying a good enough lock but also finding something to lock it to depending where you intend to camp.

Also consider how you plan to navigate, as in it's more of a pain having to keep stopping on a bike to pull a map out than it is when walking, and it's probably easier to overshoot turnings etc. if you're not forewarned about them. A mapping gps on the handlebars can be really useful, but failing that a mapcase mounted on the bars can really help you keep track of things.

Edit: My post crossed with yours above. I wouldn't like to try to ride with a 55 litre pack. Does your bike have a rack? Even without panniers you could potentially split the load by lashing the tent or sleeping bag or mat (or all of them in a holdall) to the top of the rack.

I'm just back from my first atempt at bikepacking and have the following tips;

1) make sure you panier bags are secure to the rack.

2) make sure your panier rack is secure to the bike.

3) spare straps/bungee cords are great for when tip 1 and 2 fail.

Further from the above, note that all racks are not created equal, and the bouncier things will be the more you want one that's "more equal than others".  Tubus and Blackburn have very good reputations for being genuinely tough.

And all pannier hook systems aren't created equal either.  I personally like Ortlieb which automatically lock on to the carrier when you let go of the carry handle.  The bottom is only secured by a hook to go around the back of one of the carrier stays and a more active attachment may work better over really rough stuff.  Hooks which can be padded out to best match the rack tubing stop things moving around help.  If possible taking your bike to choose is a good thing, though sadly the case that good selections of luggage are often hard to find in the shops in the UK.

Pete.

 i bet the pre-edited version was better...

 You might want to have a small backpack with your valuables in, but even that gets your back warmer. Panniers and a small bar bag were the way to go for me, but some also go for a largish saddle bag.

Although it adds weight to my Tourer I did find a double back stand is worth it as leaning bike often falls down with panniers and laying a bike down gets the panniers dirty/wet.

My local bike shop told me to forget about front wheel panniers.

I am planning a trip in the Highlands so I insured my bike fully with bike rescue etc. I had to provide a bike lock to their specification and it is heavy.

My biggest worry is broken chains and split tyre walls so I do carry a chain link extractor and a tyre boot for sidewall repairs.

Cycle chat.net has lots of useful advice.