The last roll of a shared supply is often where an unstated agreement becomes visible. One roommate assumes the other will replace it; the other thinks it was a personal purchase. Start by naming what is actually shared. Living in the same room does not make every item on a shelf communal.
Choose a short list together. It may include ordinary items used for a shared task, while personal toiletries and course materials remain separate. Follow housing rules and product instructions for anything you bring into the room. Do not let a practical shopping discussion turn into an assumption about what another person can afford.
Decide how replacement works
Use an arrangement everyone can explain in a sentence. You might alternate a particular purchase, split agreed purchases using a private record, or each provide different items. The best option depends on the household. Avoid a complicated accounting system for a few small supplies if a simpler agreement feels fair to everyone.
Set an agreed replacement cue. An empty package is sometimes too late; opening the last spare can be a better signal. Put the cue where the item lives. A short list on the inside of a cupboard may work, provided everyone actually looks there. A message in a busy social chat may disappear.
Write the item precisely enough for someone else to buy it. “Desk wipes” may refer to several products with different intended uses. Keep the label or exact product information when compatibility matters, and follow the relevant instructions. Do not mix leftover products or transfer them into unmarked containers to save shelf space.
Keep the purchase record small
Record the date, item and agreed contribution if you share costs. Keep receipts long enough to resolve questions, using a private place rather than a public board. Discuss a change in brand, quantity or arrangement before treating it as a bill the other person has already accepted.
Allow either roommate to say that a purchase is outside the agreement. Someone may prefer their own item, have a different routine or be away for part of the term. Revisit the arrangement directly instead of trying to infer fairness from how often a bottle appears to have been used.
Leave room for mistakes. If two people buy the same thing, decide whether the spare can be stored safely and used later. If a replacement is forgotten, solve the immediate need and then check whether the cue was visible. A small process problem rarely improves through a running list of personal grievances.
Give the supplies a definite home
Keep shared items together where both people can reach them without searching private drawers. Leave labels readable. Store products according to their instructions and keep access routes clear. The storage space should fit the quantity you actually use; buying more is not helpful when there is nowhere appropriate to keep it.
Before a long break, check what will remain in the room and what needs attention under housing instructions. At the end of the term, agree on who takes remaining supplies before packing begins. The same question of ownership that caused confusion at the start can return at move-out.
Review the list after a few weeks. Remove things that are not really shared and adjust the cue for anything that keeps running out. A workable agreement is one both roommates can maintain during a busy week, without appointing one person the permanent household supply manager.