How do I make the best of my chance to speak with senior leadership?
I don't think this question is too broad: OP is asking about speaking in a specific situation where OP is being honored. I admit it is opinion based.
Speak with your boss so you can get a feel for what it will be like.
Ask who will be there, and what it will be like.
Lay of the land:
There is a difference in preparation between the lunch being two senior managers and eighty other people in a loud restaurant, and the lunch being a catered affair with one senior manager per table (you would be expected to talk to a senior manager in the latter case; not in the former).
Either way, prepare in case you speak with a senior manager:
Learn what you can about each of the senior managers. What is their name, their area of control, what are their current projects?
You won't get all of this, but figure out something for each of them - even if it is who reports to them.
Prepare quick information packed sentences for use.
What are your accomplishments?
What are your teams accomplishments?
What can you say good about your boss?
If s/he says 'tell me about yourself' you can use any of them (but not all).
If s/he says, "Hello my name is X" then say, "My name is Nimesh, I work for [boss] in [boss's area] we are under [you - or which Sr. manager also at event]." Then tack one of your elevator sentences at the end, stop talking, and wait for them to ask about something you said or move to the next person.
If (after a pause!) they don't say anything, but don't move to the next person, you can ask a question or make a statement about them like "Someone told me you went to University X. I did too, what was your major?"
If you are in an intimate enough setting that you have a conversation with a senior manager act interested in them and ask questions. But don't ask personal questions unless you're leading to a connection you know the two of you have - "Do you like football?" and "I hear you went to University X" are fine... but "I hear your spouse is a pain in the butt, so is mine!" is not okay (especially if it is true).
In this setting the goal is to gently get them talking about them.
Your goal is to be like a talk show host (specifically "Tonight Show" hosted by Johnny Carson... he almost never said anything about himself and almost never told his own stories).
You goal is not to pepper them with question leaving them with the feeling that they are being interrogated by the police.