It can be news on topics you're interested in, blogs on topics you're interested in, comics, subreddits, etc. To give an idea, I follow:

• Ars Technica for tech news
• NASA for space news
• Local blogs on food/events/news/ going on in my city
• RockPaperShotgun for gaming news
• "A Collection of Unmitigated Pedantry" for blog posts from a history professor
• Richard Y Chappell for blog posts from a philosophy professor
• A few YouTube channels
• A few niche Reddit feeds
• XKCD for comics (most webcomic artists have an RSS feed)

Depending on your RSS app, you can also follow podcasts. I use InoReader for the above but I prefer a dedicated podcast app. There's good/entertaining RSS feeds on the internet if you're willing to curate it! It's nice to get away from internet comments.