Don't worry about it.
Especially in Yellowstone. There will be about 5000 people camping and cooking within spitting distance of you, so your cheeseburgers on the BBQ won't be anything special.
And if there is a wayward bear getting close to a human center there, chances of you being the first to see it and it not already being intercepted by the rangers is very slim.
Even if you're in the back country, bears do not generally seek human interaction unless they are lacking for food sources.
Yes it happens, but I'd liken it to the probablity of being in a car accident. Divide the number of days you drive by the number of accidents you've been in. Apply the same % to the number of days camped in bear country.
Not saying to smear your picnic table with bacon grease but the chances are slim based on my experience with a lot of time living and camping in bear country.