I sell cupcakes at a local Farmers' Market. By the end of the five hours, the icing is starting to melt. Any ideas for keeping it fresh? I was thinking of an ice pack on the top of the container.

You said you were considering putting an ice pack on top of the container. How are you storing your cupcakes?

What recipe do you use (provide name, link or ingredients list)?

Unless the frosting is perishable, I would keep the cupcakes boxed (but not in anything that's airtight because this will cause the frosting to melt).

HTH

We had a hard time with our cupcakes. We only displayed one of each flavor and kept the rest in a ice chest with ice packs on the bottom of the cupcake container. They still got a little soft. We used 100% butter buttercream.

I am using a 100% butter, buttercream frosting. I am displaying them on trays with light plastic lids, but definitely not airtight.

I too do Farmers Markets and it gets hot where I live. I find that heat is so much my enemy as the sun. The buttercream is very soft, but it does keep it's structure. (I use 100% butter buttercream too, and don't wish to change because that is what my customers like best about my cupcakes.)
I have a "tent" in which I keep my cupcakes out of the sun. I also have some curtains that I hang from the top of the "tent". Though this has been working. I now take freezer packs, put them into the bottom part of my containers, and put my cupcakes on top of those. I really haven't noticed much of a difference though. My next step is to drill little holes in the top (the ones the cupcakes sit in) to allow to see if the cold will "seep" up and chill the cupcakes better. I get my containers at Target, and use a flat corrigated board sign with holes in it to hold my cupcakes. It works well. I tried to post the picture here but they took it down of the kind of containers I used. I will see if I can find a link to them. Maybe that will help a little in what I am trying to explain. Hope this helps.

I too sell cupcakes at my local farmer's market. I find that by keeping my cupcakes out of the sun, my all butter buttercream holds up pretty well. On very hot days I only display a couple of samples and keep the rest in a cooler. If the ones on display begin to get too soft, I pop them in the cooler and take some of the chilled ones out.
Hot air rises and cold air falls so if you are trying to cool your cupcakes out side of a cooler, the cold packs need to be above the cupcakes, not below.

if you have an ice chest with ice packs and ice packs for on the top, and keep them out of the sun you should be ok. here's a tip....if you're going to keep cupcakes on the table just for display, try just frosting them with straight shortening. they wouldn't be for eating of course, but people will know what your cupcakes look like. they wont melt, and will will close enough to buttercream. When they order one, just pull a cold non melted one from the cooler (people use shortening for displaying ice cream and frosting on "beauty shots" and food photography)

The melting point of butter is 85°. So I won't use it in summer, as it's not unusual for it to go over that on any given day. I only use all shortening in summer, then use a combination of butter/shortening the other seasons. If you are going to use butter in warm weather, I would suggest keeping them chilled in a cooler. Maybe make a few dummy cupcakes out of foam and more stable icing that you keep on display. Keep them and use them from week to week, only selling what's in the cooler.

I do know that hot air rises and cold air goes to the bottom. All I am saying is that it works from me in 90 degree weather. It is the SUN that is the problem with my SMBC, not the heat. I won't change my recipe because that is what everyone likes. It would be compromising my product to change. Consistency is what customers look for.

Thanks for all the ideas. I am going to be trying a few of them.