you should be able to get 2 to 3 snacks per meal credit...ask before you start grabbing them. If you're driving and have a cooler, you can take things like yogurt as snacks (we've done that!) If you're flying, go for the prepackaged/sealed items. The mickey rice krispie treats travel well either way.
Our favorite thing to get with leftover snacks when we're driving is to get those yummy cinnamon rolls...we've taken as many as 4 of those with us. Great reheated for breakfast the next day.
Another thing you can do, depending on what time you leave...get lunch to go, even if you're flying you can take food with you. Sandwich, chips & cookies will travel well & you can get that for a meal credit. Course airport security won't let you take a bottled bev. through the check-points.
Oh, this is funny...just looked back at your post...you're NOT driving to Australia, lol.
So go with the sack lunch if the timing works out well. Otherwise, prepackaged goodies to take back as treats for home.