Sorry to hear you've lost something.
If you lost an item of clothing then these are kept in the Students' Union for a minimum of 2 weeks. Please come to the Students' Union Reception (by Teas and Tees) between 8:30am and 5:30pm.
If you lost something valuable such as keys, cards, jewlery or a phone then these are taken to Security at the end of each day. If you lost this item in Rubix then it will have been taken to Security at the end of the event.
If you lost something on campus then please go to University Security in Senate House. If you lost an item in the library then you could also try the information desk.