Question: I work in an office with 8 people.

We have no allocated seating. Which I am quite cool with. However, recently the tidiness has gotten quite out of hand. Papers, coffee stains, and some brochures scatter over the tables.

It's quite a rude shock when I almost put my laptop down on someone's old coffee stain in the morning.

Now my daily ritual is to wipe away all leftover hairs and dirt and choose an area that has less clutter.

We have introduced individual shelf compartment for us to store our personal goods. However, most of them still do not have the habit to clear up after themselves when they leave at the end of the work day.

I am quite concerned about how to keep the cleanliness, and would like to know if anyone has any experience in maintaining cleanliness in a free seating plan office?

Answer: 
You didn't mention any communication with the other 7 members of your work space, so I would suggest that as a first step. 

This is very similar to sharing an apartment with roommates, or having a common area. Sometimes you just need to set out rules for everyone to follow to maintain cleanliness. You could even provide some cleaning supplies as another person suggested, but cleaning up should be everyone's responsibility.
It's the <https://en.wikipedia.org/wiki/Tragedy_of_the_commons> .

Make it the Owner's problem, everyone's problem, or keep it to yourself (see who cracks first).

Don't be Felix and live with Oscar.