I got an invited to a round-table lunch where there will be execs in my field.
How do I make sure I can turn this into a fruitful and effective networking opportunity?
What kind of questions should I craft to ask at the round-table lunch?
Is there any incentive for these execs to help you? e.g. if they're at the same company, they naturally have a motivation to answer your questions and mentor you, since it indirectly helps them.
You need to find common ground: If they're just celebrity industry veterans, it'll be hard to get something tangible from them.
One idea is to have a concrete idea or proposal for them. The first thought that comes to mind is an invitation that you could profile them for your blog, or invite them for a talk. You can use the event as a jumping off point for a 2nd interaction.
Another approach is to offer something of value. Share an insight or project that they'd want to know more about.
There are some great answers here: How to network effectively in a tech event?