Hey Christine
I have lived in Jamaica 3-6 months on a couple of trips over the years, and I'm back and forth very often. (once or twice a year)
You definitely need to pack lots of toiletries! Your shampoos, lotions, toothpaste etc. these things that we can get in the £1 shop or $1 store are expensive in Jamaica. So go crazy on toiletries. Razors, tissue any and everything.
Perfume is also extremely expensive in Jamaica.
As for barell packing the essentials would be tinned food. Tuna, mackerel, sardines sweetcorn, baked beans, coffee and any other tinned food. Dried food is also necessary. Rice, nuts, pasta, flour, sugar etc. Oh and pack oil. This will all come in handy for storms or shortages.
We packed all this and so much more inside our last barell, but I would say these are a must.
Pack little sweets or non perishable things that you will miss from home. Jamaica don't always have what you fancy and if they do, with it being an overseas brand you gonna pay silly prices.
I packed water and fruit juice. Although there is quite a range of juices in Jamaica, in store the real juices tend to be expensive
Hope I've been a help.
Kind Regards