Tough to answer not knowing what you are making. Kits, fruit, or juice? I keep the following on hand and make mostly fresh pressed grape wine, with a few fruit wines from puree or fresh.
acid increase: Tartaric for grape wine, acid blend for fruit.
to reduce acid: potassium bicarbonate, calcium carbonate.
yeast energizer, yeast nutrient, extra yeast
tannin,for taste. pectin enzyme for extraction and clarifying of fruit.
finning: everyone has their go-to but, tough to beat superkleer, sparkolloid, and bentonite.
extra sugar potassium metabisulfite (K-meta) potassium sorbate.
I'm sure others will chime in, I have never made a kit, but assume everything is included.