Most that have never come onto a reservation think that there isn’t any modern conveniences, but I beg to differ. There might not be a huge variety of options, but Pine Ridge for example has two gas stations (Big Bat’s and Yellow Birds) and a super market (Sioux Nation). It might be a bit more expensive, but you can find your hygiene items, gas, food, etc. This will save you space in your travel bags and give you the ability to minimize weight for carrying things on your mission trip. Minimize all you can, it makes for good travel!