Oh wow! ME TOO! So thank you for making this post because I also want to know >.< I have downloaded a lot of other asset packs on the website to see what they contain for ideas. I also found this helpful!
https://www.spriters-resource.com/
It's a website where you can download popular pixel game sprite sheets and see the different things games contain so you get an idea. I really liked the stardew valley ones!
https://www.spriters-resource.com/pc_computer/stardewvalley/sheet/88632/
Look at this one! It shows you everything you need to make an outdoor area and how neatly its lined up in stardew.
I really like the idea of having a solid base asset pack with enough to make an awesome functioning game with, then having add ons for extra levels or environments/ extra stuff so that's my current mission ^_^
I have also found that making such a pack that contains all the base things for a game is a lot of work... I also have a job and go to school- so I am trying to break my project down into manageable parts and release 2 week regular updates with new things. I am hoping in enough weeks time I will have it all haha.
~Lavender