100% fabric, batting & thread are so obvious I won't list them... Oh, just did...
I do a half dozen or so bobbins at a time when I run out - I've got at least a dozen, so have them in taupe and grey at all times. As I'm a gadget lover, it comes as a huge surprise that I don't "need" the Sidewinder, lol, but I have enough bobbins that I don't often have to stop midstream. I do have friends who swear by them, though.
I DO love my Creative Grids rulers. I've gradually picked up several sizes, although could live if only the 6 1/2 X 24 was available. My Omni grids, some of which are brand new, and my Fiskars ones are rarely touched any more.
Rotary cutting mats & cutters. I'm one of those old enough to remember starting my first quilt (note I said "starting" as it was never finished) w/ templates, pencil & scissors. My Olfa one is most used, Fiskars is okay.
My sewing machine! I'm fortunate enough to have a Bernina, love it almost as much as my children and can't imagine ever changing. This was my treat after my father's death (inheritence money), otherwise I'd never have been able to buy it. It's over 10 yrs. old and still like new. I do kind of like the BSR's that are now available, but won't spend the money to trade. As long as I had an accurate, non-thread eating machine, though, I could get by. For me, hand sewing is a no-no, except for binding.
An iron that gets hot, stays hot and can be used with or without steam, as I press everything as I go. Wish I had a dedicated sewing room where I could have a Big Board (although it'd probably be homemade, as they are ridiculously priced!), but with my combo family/sewing/computer room, my ironing board has to come up and go down when needed.
So my basics are fairly basic - no sergers, no embroidery ability, no cool tools. Although I could always be convinced if somebody mentions something new!