Most consumer electronics don’t come with the cables, because cables are a high-margin, high-markup item. Many people don’t know that. And many people give and receive consumer electronics on Christmas day.
If you want to be a hero, I recommend paying Monoprice a visit. Monoprice sells all of the most common cables at deep discounts. I recommend picking up a couple of the most common types of USB cables and at least one HDMI cable to start with. If you think of others, go for it. For around $20, you can build up a sizable emergency kit.
And if this is the first you’ve heard of Monoprice, pay them a visit. They’re the best source I’ve found for inexpensive cables of reasonable quality, and if you want premium cables, their premium offerings are still reasonably priced.