Woodsmoke works well. When I was a young lad, I once spent a week in the North Woods of Michigan in June without any modern gear trying my hand at "living off the land." The hordes of blackflies and mosquitos lived off of me, until I figured out that the best repellent was to keep a smoky fire going around the clock.
For the sake of experimentation, I had also been ingesting whole cloves of garlic—prior to and during the trip—to repel bugs. The odor was so overpowering I was certain that I'd become spicy bait for a black bear. Several "baths" a day in the river were required as I couldn't stand being in my own presence. I've also tried B1 Thiamine, brewer's yeast, and other natural "internalized repellents" but haven't had luck—maybe it's my body chemistry as some of my friends swear by these.
I have also done the Rambo mud-method, where you coat yourself with an inch-thick layer of muck or clay from head to toe. This requires constant application and the vampire bugs eventually find some chink in your earthen-armor. But it works better than nothing.
If you are lost without bug-spray, build a smoky fire (using wet or resinous wood), keep covered with your clothes, and apply some heavy mud to any exposed skin.
Is any of this a subsitute for being prepared with decent bug-spray? NO. These are merely makeshift methods if the chips are down. Carry insect repellent with around 30% deet, a quality headnet, and you should be fine. These latter two items are must-have pieces of survival gear if you travel in the North Country, Canada, Alaska or the tropics.