Most children love building towers or structures with building blocks, but taking them a set of blocks out to a restaurant or on plane can be impractical.  So why not switch the blocks?  Instead of wooden ones, why not create your own using cut up sponges?

I got sponges in different sizes and colours from the local supermarket and then cut them up into different shapes.  The added bonus of using sponges is that if you need to wipe something up, or clean a child you now have a bag of sponges to help.