What is your "can't do without" .vimrc configuration?

Vim
1

Personally i really enjoy Gary Berndhart’s InsertTabWrapper() method → 

function! InsertTabWrapper()
let col = col('.') - 1
if !col || getline('.')[col -1] !~'\k'
    return "\<tab>"
else
    return "\<c-p>"
endif
endfunction
inoremap <tab> <c-r>=InsertTabWrapper()<cr>
inoremap <s-tab> <c-n>

I’d very much like to hear yours!

2 
set backup

You don’t think you need it, especially with persistent_undo and Git, but trust me: backup is your friend.