That is a fantastic question, and one that I have put a lot of effort into.
I have a template description that includes an immediate call-to-action to subscribe immediately followed by a series of links to various affiliate sites (which cover any questions anybody might have about the stuff we use). Next up is a link to the video that currently has gained us the most subscribers and a another to a popular playlist followed finally by contact info and music credits.
I highly encourage the use of Affiliate links, we see some solid returns from that and it can be done at just about any level of growth you are currently at. That having been said be mindful that Amazon require you to make multiple sales in a 90 day timeframe. It's ok if you don't; you will simply need to make a new account. But when you do that you will need to go back and update your affiliate links in EVERY video that featured them... that can be daunting so be organized and prepared for this in advance.
Also I suggest using a link shortener to keep your description tidy. The last thing you want is to finally get someone down into your description to look at affiliate links only to lose them because it's a disorganized mess.
That's more or less how I do it.
First line is my subscribe call to action with the ?sub_confirmation=1 thing at the end
second line is mentioning my gaming channel which I've done next to nothing with yet lol
third section is my "sawag" and merch
4th section is my amazing affiliate store
then my affiliate disclaimer
then last I have my socials attached.
Just keep in mind, any email you decide to attach, you WILL get scams and spam sent to, and if it's a hotmail email, you'll see constant login attempts so generally I'd advise against having an email in your description just to avoid the scammers and spammers.
I include my instagram and twitter, that way if anyone wants to reach out for business, I can vett them a bit easier.
I've started going through older videos to be sure to add some playlist links and related video links as well.
Also, never underestimate the power of emojis for the description section. I borrowed Nick Nimmin's description for inspiration for my layout and emoji use.
(oh, but in terms of link shorteners, make sure it's a known one. I actually avoid link shorteners because I can't be sure where the link is going to take me otherwise and there's a trust issue there, so I tend to NOT click shortened links, so thus, I don't really include shortened links in my description either)