If your doing Prov. Writs the CookeryWiz Add-on will save you tons of time once you prep your bank.
Once you have this add on loaded and food from below list made and placed in your bank.
Grab your Prov. Writ quest, open your bank, the add-on pulls the food out of the bank for you, run and turn in.
If your tuning in Prov Writs in Craglorn and Coldharbour then your getting Prov. Bag VI & V as a reward.
The foods needed for VI Writ to keep in bank...
LVL - Food - Prov Pack Reward LvL
VR5 - Arenthian Brandy - VI
VR5 Pickled Carrot Slurry - VI
VR5 - Fresh Apples and Eidar Cheese - VI
VR5 - Khenarthi’s Wing Chi - VI
VR5 - Sipping Imga Tonic - VI
VR5 - Argonian Saddle-Cured Rabbit - VI
For Prov. Bag V Reward, Food list to keep in the bank...
LVL - Food - Prov Pack Reward LvL
VR1 - Aetherial Tea -V
VR1 - Millet-Stuffed Pork Loin - V
VR1 - Orcrest Garlic Apply Jelly - V
VR1 - Grandpa's Bedtime Tonic - V
VR1 - West Weald Corn Chowder - V
VR1 - Comely Wench Whisky - V
If you're level 50 in Prov. Skill and not VR1 then you should be turning your writ into Coldharbour.
Talk to the GroundsKeeper in Coldharbour she close to the Gate near the bank, take her intro quest. Once that is done, you'll be able to turn in Prov. Writs Bag V there in Coldharbour @ the Mage Guild Locus.