Sitting, yes. Crawling, maybe but probably not. Eating table food? No.
You'll probably just be starting solids, so you'll need to bring or buy them there. We were still on cereal flakes + breastmilk at 6 months with all 3 of ours. (If you're nursing, you'll need to bring your pump or be efficient at expressing in order to mix the cereal concoction.)
6 months is also the age where babies start to get very distractable while eating. Again, if you're nursing, this is an ideal age to seek out the baby care centers because that baby will be quick to turn away at noises and interesting things to look at and a quiet, controlled atmosphere helps get you through that time period.
Your baby will likely be old enough and strong enough to start using an umbrella stroller, but he still may be fairly slouchy.
He probably won't need much entertaining in line. There's so much to look at, and that will keep him entertained. If you're going during the summer heat, be aware of that. Use sunscreen formulated for babies (because they stick everything in their mouths!) and a hat. Try to angle the way you stand so he is out of the sun. (This is relevant in some lines, too, like Dumbo.) Watch for heat rash and signs that he's too warm. There are plenty of cool places to duck into if you need a break (restaurants, shops, shows).