Lambing kit: latex gloves, lubricant, 10% iodine for dipping umbilical cord; castration rings and applicator; colostrum sachets, bottles and teats, milton; mini eartags; notebook; giant torch and head torch; binoculars.
Injectable antibiotics - both a penicillin based one and Terramycin, both long acting; Calciject; syringes of various sizes including a 50ml with long 'catheter tip'; various needles; sharps bin. Hibiscrub or Savlon type antiseptic scrub. Old towels.
General kit: Antibiotics, syringes and needles as above; Calciject as above; gloves; blue spray; antiseptic scrub; Sorgene for disinfection of surfaces and boots; 'Golden Hoof' for bad feet; white spirit or meths for cleaning foot shears and tag applicators; foot shears and daggers; Hand shears; Glucose; Panacur (or other wormer when we swap); Crovect; UK 'bubblegum' ear tags and applicator; brush and sponge for cleaning up mucky bums.
Vets number on the mobile.
General: Hay; straw; Crystalix buckets; Sugarcorn buckets; Carr's 'champion tup' coarse mix (rather than ewe pencils which are too high in protein for our primitive sheep); a large assortment of buckets for water, carrying feed, tools, lambing essentials etc.
From the house: Digestive biscuits; bandages and tape; dressings
I'm sure there's more

This isn't really a first aid kit, just everything we use for the sheep, but what you need in an emergency depends on what the emergency is, and could use almost anything listed.