And assuming this is a 'school project' (it really does sound like one and I wish people would just say it is rather than trying to avoid this fact) it's not actually about being creative, it's about reading the question and then solving a problem in the simplest way... in other words it's about showing you not to overthink a problem.
If you take what you've written literally (and I assume I've understood it correctly and you've not missed bits off - full brief would be better than how you interpret it) the answer is a hinge + handle to open/shut. It doesn't say anything about needing to stay open or that you can't hold it open, it doesn't say anything about you needing to be inside the box when it's opened either. So the 'simplest' solution is being on the outside of the box and 'opening' a hinged flap, total cost in the UK, about £1....