Equivalent of "former" and "latter" for more than 2 items

You can say first and last (without one).

Of winter, spring, and summer, I find the last most enjoyable.

I don't think there's anything inelegant about first or last. You can always use ultimate, penultimate, and antepenultimate if you want to be certain no one understands you.

Interesting question. First and last will do, but suppose you wanted to refer to the middle option, or the fourth option?

Consider for example a scenario where a party of adventurers must choose from a list of options;

• Go forward into the forest, singing a song of sixpence
• Go back to base to retrieve some hats
• Go back to base to dispute the pronunciation of the word "tomato"
• Stay put, weave baskets, and hope for rescue
• Stay put, weave baskets, and try to summon a helpful genie

Now if I were in this party considering these options, I might suggest we take the second option, but it is far more likely that I say something like we need our hats, implying that we should take the second option where we also go back to base.

In other words, with more than two options, the most elegant way is to refer to the unique attributes of the option. In fact, with just two options I still think this is more elegant than former and latter since it relieves the reader of the burden of remembering which is which.

There are other words you can use in place of "first" and "last" - for example, "foremost" and "lattermost" - but whether that is more elegant, or just more pretentious, could be debatable.