I don't usually wear a sporran with my tartan Sportkilt because, when I wear it, I'm either lounging about the house or running up the side of a mountain. For other purposes (pubbing, dinners, parties) I tend wear a sporran with my tartan kilts because it is a practical item for holding my things and, to my eye, completes the look.

When Riverkilt goes sporran-less in a tartan kilt, I think he might wear a fishing vest that has lots of pockets for his stuff. A Freedom kilts tartan model with pockets would achieve a similar functionality. I don't, however, prefer the look of a tartan kilt without a sporran, even with boots and a tee shirt...

For a more modern look, perhaps you might investigate contemporary sporrans like those from http://sporran-nation.co.uk/. Alternatively, there are bound to be non-bespoke sporrans with similar designs if you search a bit.