Dirks were effective weapons in war as well as a useful tool for everyday tasks, including eating. They were also more affordable than a sword. Taking these things into account, it is easy to see why it was hard to find a Highlander without such a weapon. What is a dirk? More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.