Having special troop patches is great for the Scouts. While large troops have an advantage, in that they can order larger quantities for a lower price per patch, you can order as few as 25 patches from many companies. We have used several of the patch companies that advertise in the back of Scouting magazine. If you don't have an artist in your troop, many patch companies will have their artist do a final design from your rough sketch.
We have always designed a commemorative patch (BSA calls them "temporary" patches for the right uniform pocket) for our annual troop High Adventure Trek. We have also designed patches for our troop neckerchiefs, for a troop hat, for our special Master Camper Award, and for special troop anniversaries.
Our troop high adventure treks, expeditions, and 'SuperTreks' have included backpacking, river canoeing, voyageur canoeing (lakes & portages), bicycling, and sailing, with a special patch for each one.