My friend makes a sandwich for me. I say:
Wow! Thank you so much for making it/this for me.
Are both okay?
They both seem fine to me.
However, I would just mention that it would depend where the sandwich is when you say it.
It would seem odd to say "Wow! Thank you so much for making this for me" if the sandwich is out of sight, say in the fridge, or in another room. If you're eating it , or it's in you hand, or near you on a plate, or you can see it and point to it, then it's fine.
However, "Wow! Thank you so much for making it for me" would work wherever the sandwich happens to be.
Last edited by Eckaslike; 03-Aug-2015 at 20:39. Reason: Removing typos.
(BrE first language speaker.)