I love bringing cupcakes to events since they don't require plates, forks, or major serving utensils and involve relatively little clean up. But unfortunately, cupcakes are not immensely portable. I've tried several different routes over the years, and here are some of my thoughts:
1. Tupperware cupcake courier
This holds an odd # of cupcakes - 18, which is really strange to me. Cupcake mixes generally make 24, even muffins usually do at least 12, so it's pretty strange to build a carrier that takes 18 cupcakes. The bottom has round cavities for each cupcake that are less than 1" deep, and therefore kind of useless when it comes to keeping the cupcakes upright and secure. It also flips to convert to a 1/4 sheet rectangular cake, though I've never used it as such. I appreciate how well Tupperware makes the pieces snap together, they feel relatively secure and I don't worry about the bottom falling out, but I do wish I didn't have to work so hard to keep the cupcakes from falling over and ruining the frosting.
2. Snapware Cupcake system
I scooped up one of these at Costco, mine came with 3 layers and supposedly you can hook up to 6 together, though I can't imagine that would be very easy to carry. Nor do I believe for a moment that the handle would support it, even with just 3 layers I felt it pulling and warping, and it sucked in a big bunch of air every time I picked it up and used the handle to support the weight. This has an insert for each level much like the Tupperware version, with spaces for 12 cupcakes in each level. But again, the cavities are less than an inch deep, so with this carrier as above, any jostling tipped the cupcakes out of the cavities and into each other. I had high hopes, but it's really just a less expensive and more stackable version of the Tupperware one.
3. Disposable cupcake containers
This are awful for the earth, I know, but they are really the best way to keep cupcakes secure and upright. Sometimes you have to be careful that there is enough frosting room, and there aren't a ton of places to get them at a reasonable price, but they are worth it for many occasions. I've found them at Lynn's Cake & Candy Supply and used both the half dozen (good for bake sales) and full dozen sizes. Next I want to try the individual cupcake holders, but they're usually close to $1 each, which really ups the price per cupcake.
4. Tupperware Pie Holder
I've found that the 12" rounds, marketed as pie storers, are actually a great size for keeping cupcakes. They are deep enough to allow a decent pile of frosting, and you can load them up so that they fit snugly and keep each other from tipping over. The Tupperware seal means it's airtight, and I really like to use these for cupcakes I'm refrigerating before travel. In general, I've had much better luck with cupcakes surviving travel in this container than the others.
5. Window Box
I picked up a package of these at target and they really are adorable...and spendy. Over $1 each seems difficult for a single serve and quickly discarded item. The cardboard box is easy to set up with an insert to set the cupcake in, it seemed to keep things relatively stable.