I registered a couple of domains, and consider buying a few more, simply because I'm afraid they would be taken by someone else and I plan to create websites for them in the distant future. Right now they point to the information page of my registrar. Could I put them to better use for the time being without much hassle? Is it worth creating very minimal domain-related content and hosting it? Would that help SEO in the future or the contrary? Is there a chance of getting some adverts for a website stub, so that I could generate some income towards hosting costs?
You can park them but it's common for Google and Bing to remove parked domains from their indexes when they notice this. It can be a problem/delay getting a domain to re-index with new content after this happens. Note that parking doesn't typically bring in much money at all.
If you want to develop these domains later, then I'd recommend creating a simple "coming soon" type website with about 10 pages or so of meaningful content and no ads. Another option is to redirect them to an active domain you own although this can also cause temporary indexing problems with search engines when the site goes online completely.