I only have one AR15 and am looking into buying extra parts that may break. I have an essential arms lower and I believe but not sure that the upper is also EA. I don’t think I have chromed lined barrel. With that being said what parts should I look into buying? I just want to make sure I’m set if a ban comes later down the road.
aloha 
and search is your friend
one from a few days ago of what seems many threads on the matter
https://www.m4carbine.net/showthread.php?t=26790
there are quite a few threads on spare parts and what to have around and also a good sticky on tools you will want to get etc…
https://www.m4carbine.net/showthread.php?t=7463