Sponsors faced growing criticism over unused tickets at Olympic venues after a number of events took place with empty seats.
Games boss Lord Coe said troops, students and teachers were filling gaps left in stadiums, while others ticketholders could be upgraded.
Events including tennis, swimming, basketball and rowing have been affected.
Tickets for double sessions, such as those for hockey, basketball, water polo and handball, are also being recycled and re-sold as people leave.
There were reports of fans who were in the Park on a £10 day pass securing £90 men’s basketball tickets for the US vs Croatia for £5.
Twitter users posted pictures of venues that appeared not even half full.
Jane Carruthers tweeted a photo at Wimbledon, writing: “Our view on No.1 - ridiculous amount of empty seats.”
Claire Howe, 25, from Cheshunt, applied for about ten events in the first round, including cycling and athletics, but missed out and will travel to Cardiff to watch the final Great Britain men’s football group match.
Ms Howe, a marketing executive, said: “It’s unfair that you apply, you don’t get tickets and then see you all these empty seats.
“The Games is all about inspiring the next generation so these places should be given away to children from local community.
“They should be finding out why his is happening and maybe fining people who didn’t turn up, even if they are corporate - it’s not fair to the people who applied.”
Lord Coe, London 2012 chairman, said: “It’s not easy to ask people (in the accredited Olympic family) at the beginning of the Games to ask people exactly how, where and when they’re going to be in those seats.
“This morning was a very good example, we looked at gymnastics, we could see at this moment there are empty seats in the accredited area - the rest of the venue is looking pretty good this morning, there’s a good atmosphere. So we were able to move those troops from - I’m not quite sure whether they were on a rest period or whether it was a transition from work through to a rest period - but they’re sitting there enjoying the gymnastics. We can and we have moved them in there.
“Yesterday, we got pre-accredited students and teachers from the local boroughs. We were able to put 115, 120 into a venue.”
He added: “We can clearly sell more tickets, which we did yesterday. We sold something like 1,000 tickets over three sessions. The other thing is we can tactically upgrade and move people. On handball yesterday, we recycled just under 300 tickets, about 283 tickets, and they went out to adults at £5 and children at £1.”
Shadow Olympics minister Dame Tessa Jowell said: “Anyone who is lucky enough to have tickets to the Games should either use them or give them up.
“I am pleased to see that unused tickets are now being distributed to members of our armed forces, local teachers and students. It is important that this process is stepped up to ensure that every single available ticket is offered to somebody who will use it.”