I have a possibility to buy a box of 50 Bic lighters on a discount and with free shipping. Since I don't smoke, I'd use them only for building fires in travels. For how long could those lighters lie on a shelf before the gas evaporates (if it does)?.. Of course I might wrap them tightly in plastic foil, but I'm guessing it won't help much.
Assume that the gas won't evaporate in your lifetime. Those things are tightly sealed and last essentially forever. I've found half-used BIC lighters washed up on riverbanks that still worked. Of course you may find that some in the pack are defective, not full sealed, or with crooked nozzles so the flame burns your fingers every time, etc.
Single-use lighters have a much longer shelf life than the fluid in a pre-filled refillable lighter. Exactly because they aren't refillable, they don't have openings for the lighter fluid to evaporate. I have a lovely refillable engraved Zippo, but every time I go to use it the fluid has evaporated, so I end up using a cheap disposable lighter.
So, while I hear everyone who commented that disposable lighters are wasteful, what about all the lighter fluid that evaporates from an infrequently used refillable lighter, if you're refilling it every time you use it? IMO, for infrequent use, a disposable lighter is the best balance of price and reliability, and not substantially worse for the environment. That said, you don't need a 50 pack unless you're prepping for the apocalypse. I've been using the same three disposable lighters I bought 5+ years ago. I keep two or three in my camping gear, and they work every time. They are cheap and ubiquitous; you can buy multiple for a few dollars at the checkout counter of any gas station, grocery store, convenience store, drug store, what have you.
Edit: Chris H's comment reminded me that I actually have a different refillable lighter that holds its fuel reliably well. So I guess the real moral of the story is if you get a refillable lighter, get a brand that's not known for leaking.