Just got back from 6 months in South America and the single most valuable item in my rucksack was a tupperware box. I saved so much money by cooking enough food the night before to last for lunch or supper the next day. It also meant I could go further off the beaten track by not worrying whether I would be able to buy lunch as I would have a healthy portion of pasta in my rucksack. It was also really good for transporting sachets of salt, pepper, herbs, tea bags etc from hostel to hostel.
It certainly isn't the most exciting thing but having a tupperware box made massive difference.
All over the world!
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