I found a competition on a packet of Doritos today, so had a look at it and it told me to go to a particular website to enter.
The website isn't active yet, as it says that the competition starts on the 23rd of June, but when it does, it will have a major prize and daily prizes.

Major prize - return trip to LA for 2 people, with 5 nights accommodation, 10 laps in a "luxury" super-car, and fly a combat/fighter jet. Worth AU$14,000. Entries must be in before 2nd September for the main draw.

Daily prize - Transformers cooler, worth $115. Drawn from 24th June to 2nd September of the previous day's entries only.

Entry is through the website after purchasing a participating product (perhaps with the barcode), with 1 entry per pack... maximum 3 entries per household per day.
I don't see any unique markings inside or outside the pack, so it may well be possible to enter multiple times from the one pack, within the daily limits.

The competition appears to be open to Australia and New Zealand.

Since we have the jump on this, I would hope to see a number of the early daily draws go to members here before too many of the general public start entering... like we did with that Target DOTM competition that had those toy prize packs.