What country should I combine in a Fiji trip?

Hi. I am planning to visit Fiji for the first time and I was considering adding another country so I could visit two countries instead of one. What are possible options?

I am planning to visit on Jan or Feb and travel from the US. I am considering allocating a maximum of 9-10 days for this trip. I have no budget issues and I enjoy different travel styles including beach and city but I usually do not like to spend a lot of time in a single location (no need to "relax" 5 days in a same beach town!) which is the reason I am contemplating adding another location rather than spending the whole 10 days in Fiji only.