I use the following in my kernel project: asm, const_fn, const_generics, exclusive_range_pattern, global_asm, panic_info_message, start, untagged_unions.

Of those, I could get away with just global_asm, start, and const_generics if I had to, but the others certainly make my life easier in a kernel space without an allocator.

I'll be the first to admit that some of those are "I'm just going to embrace nightly if I'm stuck on it anyway".