Aside from the fact that anything with mass cannot travel at the speed of light… Lots of fun things happen as you approach the speed of light. There’s an excellent mostly-hard sci fi novel called Tau Zero that explores this concept in depth and, despite being older, is worth the read.

(1) Time dilation (the universe and you have different clocks).

(2) blueshifting of objects in front of you. At 0.95c, basically all visible starlight in front of you has been blueshifted into ionizing radiation. Fun fun.

(3) shape distortion. You become more needle-shaped – getting very long and skinny, as observed by the rest of the universe.

(4) you become a nuke. At .99c if you run into anything, your kinetic energy related explosion would be roughly 6x the Tsar Bomba (largest nuke ever detonated) for each kg of mass. Or, put another way, each kg of your mass would impact with the energy of 3kg of antimatter contacting 3kg of matter. Boom.

Sci fi always overlooks the last one. Near light speed combat is basically firing buckets of sand at planets and blowing them up.