Would light bend the other way, if I use antimatter instead? Imagine the following setup: an antimatter straw, an antimatter glass filled with antimatter water and we have antimatter atmosphere just in case. My question is: does Snell's law still apply here as though they are regular matter, if I were to observe the straw inside the water?
 A: We think antimatter refracts light like “ordinary” matter, but we don't know for certain. As the Wikipedia article on antimatter says:

There are compelling theoretical reasons to believe that, aside from the fact that antiparticles have different signs on all charges (such as electric and baryon charges), matter and antimatter have exactly the same properties.

However, theory always needs to be experimentally verified. The Antiproton Decelerator at CERN is able to make and trap small numbers of antihydrogen atoms, and there are a series of ongoing experiments which are investigating the detailed physical properties of these antihydrogen atoms. We expect them to behave like "ordinary" hydrogen atoms, but any of these experiments could produce unexpected results which would open up whole new areas of physics (which is why vast amounts of money are being spent on them at CERN).
A: I would say no.
If everything is anti-*, also the refractive index will be. Thus, being both negative the resulting bending of light will be the same.
As an example take an electric field and throw an electron through it, the e- will be deflected in one direction.
Now, if you take the anti- of everything the E-filed will be essentially reversed but the old e- is an e+ and thus the deflection will be identical.
A: It's a no from me.
For light to bend the other way, light in antiwater would have to have phase velocity greater than $c$. This is possible in some systems (called metamaterials) but the optical properties of antiwater would have to be completely different from ordinary water - which is ruled out by existing experiments which show that positrons and antiprotons attract very very similarly (at most) to electrons and protons.   So it is JUST possible that the angle of bending would be slightly different (this is the sort of behaviour the CERN experiments are looking for) but nothing so drastic as complete reversal.
