The manding possibilities are endless when having a BBQ.
Figure out the things your child is motivated for and contrive situations for them to ask.
Instead of putting everything everyone needs out on the picnic table, only put a few things out and when you see motivation for the missing items, prompt your child to ask.
Rather than filling your child's plate with everything they are going to want to eat, give them smaller portions so they come back for more. This creates multiple opportunities for manding.
You know your child loves ketchup.
Rather than putting it on their burger, use it yourself in front of them. When they show motivation by looking at it or reaching for it, you could prompt them to request, "Ketchup".
Your child loves ginger ale, but is unable to pour it from the huge bottle. When you see their motivation for the drink, prompt them to request and then fill it up half way, rather than full, so you can create more opportunities.
Please share your ideas and successes so we can add to the list of examples.