Bear Spray

In my experience, which is a lot of time in bear country, bear bells are close to useless. Most of them are not very loud. Second bears in Yellowstone, Glacier and other heavily visited areas become habituated to humans. They are not hunted and often just don't leave even if they hear you. Bears do not have especially good hearing.

Amazon

Why buy local at Yellowstone? What's different about local vs. what's available on Amazon?

Buy it at the Yellowstone Visitor Center.

On a related note, when we were in Yellowstone, the rangers told us to talk loudly while hiking so the bears would hear us coming. When the wife finally get tired of talking, she told me to talk, so I started going "Here bear, bear bear. Here bear, bear, bear."

She was not amused. Majorly.

I have a can of UDAP bear spray. Thankfully I have not had an occasion to test it on a bear. I should mention that it says to avoid storing it in temps above 120 degrees or in a hot vehicle or direct sunlight. I suspect other brands might have similar cautions. If exposed to too high a temp, the can might discharge spontaneously. Imagine trying to camp in an RV that stinks of bear spray! So I store my can in a fridge or cooler when traveling.

just in case you're flying, you can't take bear spray on a plane. they will pull it out of your checked bag too. Getting bear spray in or near the park is convenient, but they charge more for it too. I had better luck stopping at a walmart to get bear spray there. Now I always carry it in the camper, even not in bear country as some additional human deterrent if I ever need it.

x2 Bear Bells and buy local

Get and wear a bear bell.

Far better because they'll hear you and run away long before you see them.

Metallic sounds are unnatural in the wilderness and scares animals away.

Counter Assault is the brand I have seen most often and seems to be the brand carried by park rangers. I doubt there is a whole lot of difference in brands. Just be sure to get one with a nylon holster.

Pick up a can somewhere in West Yellowstone, YNP it's self, or a sporting goods store when get near YNP. They are priced fixed from what I have seen and when I bought a can. Forget branding. You can also rent in YNP.