You should be proud!

Chances are, he’s just playing with sounds, their function in words, and how he makes them with his mouth and tongue. T, p, and k are plosives and are kinda fun to make.

It’s great that he can identify the ending sounds at such an early age! If you’re so inclined, you might be able to teach him to read some simple words. Make a game of it: get some 3×5’s and write those three letters on them. Say a word: “tight,” and have him id which letter comes at the end. Then write it and show him he’s right. He will probably start finding it (hearing it, or seeing it in writing) in other places in words, too. Of course, only do it if/when/as long as he thinks it’s fun.