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comfortable shoes--lots of muddy or rocky paths!
skirt for women--more often than not women dress modestly and in skirts
SIM cards-: buy at the airport upon arrival (ask upon arrival), get as soon as you exit customs).
Get the market leader brand-, it makes a big difference in some countries (e.g. easy to transfer minutes and money in Kenya if you're on Safaricom).
When you first arrive buy the largest possible voucher for mobile minutes: the per-minute charge is much, much lower if you buy larger denominations
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