The title pretty much says it all, I hope. I know there are other similar posts on here but I'm feeling that 16months is quite different to 20 months in terms of what keeps them amused. He's only one at the moment, so I'm planning ahead! At the moment he is shock horror entirely uninterested in TV so my safety net plan of a portable DVD player may not work...
Wow. Hopefully he'll sleep some of the way, you could take picnic style foods so time can be spent in constructing a lunch, wraps, houmous and little pieces of chicken and stuff to add to make it.. Playdough (although my ds has only just started enjoying it and he's 2).
I don't envy you. Is there no way you could break the journey up. It'd take longer but stopping for fresh air and a change of trains might be a good idea.
Buy some cheap plastic toys and wrap them up in wrapping paper. Lots of snacks. A book he hasn't seen before.
Also, my DD was the same at 1 - very, very active and wouldn't sit still for the TV. However, at around 15-16 months she suddenly became obsessed with In the Night Garden and Peppa Pig - so there is hope!