Prepare coins to put in 2x2

How do you prepare circulation coins to put in 2x2 flip? How to clean or neutralise oils and acids from the fingers? I know that we should not clean coins, but i want to neutralise or conserve them.
And one off topic question: Are cheap chinese coin capsules safe? They are a lot cheaper than brand named capsules.
Sorry for my english.

I soak mine in isopropyl alcohol (rubbing alcohol) and gently clean them with a cotton makeup pad or a non-scratch car polishing cloth. The alcohol will remove any grease but leave the toning intact

Mine just go straight into the flip or whatever. Most stuff made now isn't going to be worth anything so it's fine !

Most of the coins are from 1850 - 1970.

A quick acetone bath will remove any oil type substances from your coins. The Chinese made coin capsules should be fine (if you can find the right size).

Unless you have knowingly contaminated them I never do any prep for storage. 1850 -1970 so at newest they're 46 years old and they've been fine so far I don't really see the need to do any pre storage prep.

Thanks for the advice!
I try to touch them as little as possible. I do not know how much they have touched previous owners.
For now I have 12 2 and 5 silver reichmark (1934-1939), and 2: https://en.numista.com/catalogue/pieces11558.html (1900). These coins are slightly more valuable than other.