BBQ Day!!!! For 30-40 people, really just depends on what types of food you decide on! Grilling carne asada is always a hit for us! Of course burgers & dogs is fun also, just tweek 'em a bit. Like add teriyaki bbq to the burgers & dogs before grilling them. With burgers & dogs you will need bread, ketchup, mustard, pickles, tomatoes, onions, lettuce, mayo, etc... With carne asada, you need tortillas, salsa & thats about it... some people like onions... My recommendation is have lots of chips, dips, fruit trays out... people fill on those & when the food comes it makes a difference in time & cost! ...Also add in some sides, like potato salad, macaroni salad or even rice, or even a garden salad... Don't forget sodas, I like to put out a large cooler of water & ice, flavored with slices of fresh oranges, lemons, watermelon or even cucumbers, just slices as it's flavored water not juice! Entertainment, music is a must! Consider the space you have for games! If you have a large space how about trying an Amazing Race, you give them an envelope with clues & puzzles to figure out... Limited space, table top games are fun... we play a card game with spoons, relay races with water ballons is always fun or how about breaking out a couple hundred water balloons & go at it, with water pistols, etc... A few years ago, we broke out in an old fashioned game of tag! It was crazy fun!!! Shop the two, as both have advantages, but I always try to fill folks up on chips before serving food! It makes the difference of someone eating 3 hamburgers or 1 hamburger & chips... Have fun & Good luck!