For a long time, and sometimes still, I carry a 2' piece of silicone rubber tubing, about 5/16" ID and about 1/2" OD. Comes in useful for sucking up water from between rocks, siphoning gas, as an emergency airway, temporary tourniquet, quick and dirty lashing, and as way to blow air into a budding fire without risking the eyebrows.

If you add a barbed connector, the best are made of glass reinforced nylon, to each piece of tubing it adds a bit of weight to help get it down into spaces and, assuming other people on your crew each carry a piece, you can make longer siphons for tapping vehicles and bulk tanks. If the tubing is soft you might be able to use the connector for an emergency airway.

You can use any suitable tubing. Vinyl tubing works, is immune to most chemicals, and it is cheap and readily available, but it doesn't stretch much and it hardens with age. Latex rubber stretches well so it works better as a tourniquet or restraint but it deteriorates very rapidly if exposed to petroleum products and it is often so soft it can be difficult to work down a hole to use as a siphon and it can sometimes be too soft to use as an airway. Latex allergies can also be a consideration. Slightly stiffer tubing, like polyurethane, makes better airways but doesn't store or tie well. Synthetic fuel line is good in some ways because it is chemical resistant and fairly stiff while being soft enough to store easily. Automotive vacuum line is another alternative. Both are available at any auto parts store.

My favorite is high-grade silicone rubber. Sweat, gasoline and sunshine doesn't damage it. It handles heat well, up to about 500F, and doesn't really burn. It stretches fairly well but at close to 1/2" OD it is just stiff enough to stuff down a hole for siphoning and and to maintain an airway.

My advice would be to buy lengths of anything that looks promising and keep trying until you find something you like.