It's interesting to note that, even as aliens, the tangible things we would take back from this planet have nothing to do with manmade products. They exist naturally. No-one mentioned taking back clothes, cars, houses, money, toiletries, etc. Simone mentioned food, but based on her other answers, I don't think she meant KFC and Pizza Hut. Most likely something healthy - whether cooked or raw, from Nature's produce. Kaivalya mentioned music and also mentioned wanting a new iPod, so I'm not sure if she meant she would take the iPod with music back to her alien planet. I feel she would simply want to take 'music', the thing, the ability, the collection of notes creating melodic harmony - as opposed to limiting the experience of 'music' by having it belong to or come from any one manmade thing (e.g. CDs, iPods, guitar, etc).
I like the fact that 11 would take back "the beach", whereas I chose to take back a 'vial' of sea water as a souvenir. 11 is thinking big. But who knows ... maybe on my planet there's the ability to plant small portions of earth matter and for those 'seeds' to grow anew, uncontaminated by mankind's pollutants.
I'm sure the aliens would be in awe of Mother Nature and consider her to be the ruler of our planet. They would wonder why humans are so abusive of and disrespectful to their Queen.