
As soon as you get to the island-- stop by Costco or Walmart and buy in bulk. If you don't have a car--getting to Walmart and Costco can be quite a process and you could get stuck shopping at expensive local markets. No good.
When buying dish soap, laundry detergent, and hand soap, look for ultra concentrated items so that they last 3-10x longer.
Dish soap: Find an old soap container and fill it 75% water then fill the rest with soap. Shake gently to make sure it mixes. VoilĂ
Hand soap: Refill old container 70% water and top it off with antibacterial hand soap. I like Equate because it is cheap but smells good and it leaves my hands feeling clean.
Don't try to put the soap in first or it will bubble and foam like crazy as you try to add water.