Anything small and neat would be my preference - although I wouldn’t want to build anything myself as I am cack-handed 
Any convoy would be a great choice.
Many of us lack a soldering iron and solder 
Making them part of the giveaway would probably add far too much to the cost
I think what I’ll do is, give the option to pick a host, led, and whether or not the winner wants the light built or the parts to build it.
I think it is very cool you plan this so thorough.
But too much choice could be a bit much right? Isn’t it nice to just make a nice DIY package as prize and request to show the finished result?
Well seasoned modders cold let it pass, newbies eager to learn could be motivated to do so. It is a lot to take in when starting I have found out, to have a neat starter kit with all parts is very cool!