This is my favourite tools for making medieval garments.
Fabric scissor, paper scissor, thread scissor. Use your best scissor for your good fabrics, and the paper scissor for toile fabric, paper patterns and everything that is not so important. A small thread scissor is easy to bring along and spares the other two from to much carrying around (and laying around the house were other family members may find them)
Measure tape, long ruler and a small measure stick (in Swedish mätsticka, sömometer or fifficus). The long ruler (or just a straight stick) is very useful when drawing out long lines on the fabric. I have one at 100 cm, one at 60 cm and a couple of shorter ones, but 100 cm is best if you have to pick one. The small measure stick is very practical for folding edges, putting on trims or details and adding seam allowance to your pieces.
Fabric chalk for drawing out your pieces on the fabric.
Pins for holding pattern pieces toghether or marking things out without chalk (for example) and sewing needles of different sizes- I like to sew my pieces together (running stitches) with a slightly longer needle than I use for casting edges with whip stitches.
Safety pin to pin down sewing projects (it´s easier to sew if the seam is pinned down to something)
Seam ripper- do I need to say more? Thimbleful (fingerborg) for sewing (click at this post and watch the video if you want to know how)
Threads of different materials and sizes. The lump is bee’s wax and is used for coating the linen threads when sewing. Makes them last longer.