What are some types of affiliate links which might be suitable for that? One that comes to mind might be Amazon's affiliate program since they have every kind of product that is which could be bought in their (short) cookie span for you to get a commission. I'll use an example I saw on a YouTube video recently. The video was called Can money buy happiness? and it was done by The Young Turks, a very popular network. So because its a popular channel in which lots of views will be guaranteed for any video, they've obviously made some commissions with the links you see in the description. But overall, what do you think of such an approach for affiliate marketers?
I wouldn't recommend putting links which have no relationship to the video topic, unless you have some video which will literally get hundreds of thousands of views minimum. Even then, while making some money, you wouldn't actually make as much as you might have if the affiliate product actually related to what the video was about. Viewers will just come and go, unless they are so totally bored that they take the time to click on an unrelated link, which means their traffic quality will be horrible!
Obviously, you'll have a much higher click-thru / conversion rate if you stick to affiliate links that are highly related to your content...