I bought this mat for an international flight I was taking with my 6 year-old and filled it with several Lego Mixel sets (the ones where if you buy three in the same colour, you can combine them to make a "max"). There was more than enough space in the cinched bag that I could have added several other similarly-sized sets. I pre-opened the Lego packages and sorted the sets into plastic zip-top bags to make them easy to open during the flight. This allowed my son three individual sets to build and then provided him with a variety of pieces he could use to build his own creations later. We found the bag to be slightly larger than the tray table on the airplane, plus my son was too far back from the table in his seat to reach it comfortably anyway. We just opened the Lay-n-Go bag up slightly in his lap and he happily built away with no issues.I have read a number of reviews where people feel the bag is too small to hold much of anything. I guess that really depends upon what you are hoping to carry, but if anything, I feel that it is deceptively larger than it looks. Capacity-wise, I would say that you could carry the equivalent of a very large grapefruit in it. It would easily fit the pieces of four to six of the smaller Lego sets which, if you plan accordingly, will provide your child with enough wheels, bricks, mini-figures, and other items to create for quite awhile. Any smaller toys like Hot Wheels cars, Polly Pockets, or even puzzles (we have purchased a couple of 50-piece puzzles in small tins at the dollar store) would work well. Also, as a point of reference, we have used this bag to contain the Plus-Plus 600-Piece Basic Assortment, which fit perfectly and gave two children access to the pieces when it was open on the floor.This bag is light, but sturdy. There is a velcro pocket on the inside to hold smaller items if desired. Open, there is a considerable play area which, if you leave the string every-so-slightly cinched, will provide a slight "lip" to keep smaller items contained within its borders. As I mentioned, the mat worked adequately well on the plane, but where it has really proved particularly useful for us has been in areas where we can make the most use of the bag as an actual playmat, such as on the bed of a hotel or cruise ship, the floor at Grandma's or a doctor's office, or on a table at a restaurant. The design makes it is easy to quickly cinch back up when the activity time is done. Highly recommend!