I was recently introduced to an interesting product called the Shoemerang. This product is an attempt at addressing the problems around traveling with shoe trees in your luggage.
The product gets its name due to its unusual 3 pointed shape. Although, if you throw one across the room it does not come back, unless you hit your spouse and then comes back rapidly. Fortunately, the Shoemerang is made of foam rubber, which also makes them very light.
To put the Shoemerang into a shoe simply curve the longer point lengthwise and stuff it into the shoe as far as you can, then fold the other two points into the heel end of the shoe.
The product I received fit my 11.5 D (US) shoe fine, but for shorter shoes you can trim the heel ends to better fit in the shoe.
While the solution is lightweight, and therefore a big benefit when traveling, it does not provide nearly the support that a normal wooden (or even plastic) shoe tree provides.
If weigh was a major consideration when traveling, the Shoemerang would be useful in a pinch, but it is not a product I would use as a replacement for shoe trees on a regular basis.