I eat alone about twice a month, typically at places that have bars; I eat at the bar. I find it easier to talk to strangers than to people I know; actually more interested in them, so I wind up asking questions and learning about their lives...sometimes bartenders, sometimes other customers. It's like I'm a variation of myself, more outgoing, slightly less inhibited or worried about what others think. The liquor helps but I don't need to drink much of it. My interest in them almost never lasts longer than the conversation, so it's not like I'm trying to make friends.
If that's not an option, I read stuff on my phone, maybe from my RSS feed, maybe a kindle book.
Whether my entertainment consists of reading or other people, I try to eat slowly; the meal is 3-5x the cost of what a meal at home would cost and almost certainly will taste better, so I want to enjoy it.