I'm a fan of Seerah's "VendorMaster".
Auto-buy (for reagents, water, whatever), auto-repair, and auto-sell junk, with save lists for greys you wanna keep, and sell lists for non-greys you always wanna sell.
Also, each option is capable of being turned on/off individually (I usually have auto-sell and auto-repair on, and auto-buy turned off, but I may set up auto-buy to keep my waters topped off
)