Take my Jack Russell everywhere with me, hiking and mountain biking.
She starts getting tired at around 20km, but as she's only 5kg i do tend to pick her up for little stretches especially on the MTB.
I'm in no doubt she can walk/run/ride further than me, but if carrying her for a few km near the end of a walk saves her joints in later years i see that as a fair trade.
Never bother with a lead off-road but then she's an extremely well behaved dog and she's extremely well trained.
Only real difficulty we've had is that being a short haired dog that's kept in the house she really tends to feel the cold.
I've got a old sleeping i've cut down for milder nights, usually put her on top of my rucksack so she's off the ground.
On really cold nights then i'll have her in the sleeping bag with me, doesn't move a muscle all night and she's a pretty decent hot water bottle.
Few tips i'd give:
Keep an eye on your dog, if you know it well it's not difficult to spot when they're starting to get tired.
Spend walks training, the better trained the dog the easier it is on you and them.
Luckily our dog loves training and comes to heel, stops, sits, ignores strangers and other dogs, but still i take treats on every walk and keep up the training.
Try and caution other hikers/bikers from stroking and making a fuss, this is basically training the dog to go towards strangers, if the strangers want it or not.
If you keep the dog in the tent then spend around 15 mins each night really giving it a good check over for ticks.
Tried every tick remover on the market, by far the best i've found is the lasso type.
On smaller dogs it's really important to keep them hydrated, a little often is best.
I've trained our dog to drink from my water bladder, she stands a few cm away from the valve and i effectively squirt the water into her mouth, it's a LOT easier than messing about with water bottles.
Try and get the dog off the ground in the tent, on your rucksack or on a corner of your sleeping mat will make a massive difference.
Careful while cooking, it's not fun having your nearly ready meal knocked over.
Try and keep it fun and try a few things to keep the dogs attention on you while walking, be that treats every now and then with some praise, or kicking a stone for it to fetch once every hour or so (more than that they tend to start to get a OCD every time you kick a stone)