Tilda has a promotion for one free cinema ticket from 4kg, 5kg, 7.5kg, 10kg, 12kg and 20kg bags of rice. Tickets can be used on any day at performances starting before 5pm. They are not valid with any other offer or for 3D, special and preview screenings.
To claim your free cinema ticket, you fill in a form on the packet and send it to a Freepost address (no postage required). They will return a voucher for the ticket within 14 days. They need to receive the coupon by September 21st 2010, and you need to use the coupon by October 17th, 2010.
Your cinema ticket is only redeemable at Cineworld Cinemas (not Shaftesbury Avenue, Haymarket, Fulham and Chelsea). Tickets can also be redeemed at a few select independent cinemas. http://www.tilda.com/cinema
has a full list, and more terms and conditions.
I bought a 5kg bag for £11.25 at Waitrose. There is a recent thread on 5kg bags for £8 at Asda. I don't know if these have the promotion.
Adult tickets before 5pm at my local Cineworld vary in price between £5 and £7.