The splitting checks is very regional.
Here in our part of the Midwest, the waitress always asks. We don’t have to ask, separate checks are very common.
BYO restaurants are also regional. Never went to one until I had a child in NE PA.
Here in Michigan we buy our alcohol at the gas station, my daughter’s boyfriends from NJ are fascinated by this.
Along with fish bait, ammo for your guns and sugar beets to bait your deer. But that might be another topic for another day. 
My college boyfriend from Michigan was agog that in Illinois one could buy all alcohol anywhere from a gas station convenience store to a grocery store. At the time in Michigan you could only buy at “package stores”
When I lived in NJ there were a lot of restaurants that were BYOB, even at some very upscale restaurants because NJ towns didn’t issued many liquor licenses. It brought down our bills a lot, and also allowed people to bring their favorite wines to share. In NYC there are not as many BYOBs. I think most restaurants make their money in alcohol. When there is BYOB they usually charge a hefty corkage fee.
Agree - really love BYOB places (w/o the corkage fee which just screams of a money grab). The food prices are usually a little higher since the restaurant isn’t making margin on the drinks but that seems very reasonable to me. Just not many of them in MA.
I’ve never been to a BY O Pl. here in South Florida
Having just visited my children the only thing I bought was water and popcorn at a baseball game. My son ordered dinner in and paid for the bill without even a thought.My DIL told me that I don’t need to bring out as many gifts as I do, but bringing toys, clothes and books gives me pleasure. I’d like watching my grandson pull out one thing from the bag, like a truck, play with that for a while and then go back to the bag to see what else he can find.