Thank you for your donations.
How to change donations in this sentence? Financial help? Contribution?
What if I wanted to generalize my thanks for all kinds of helping? Could I say gifts?
A "donation" can be anything -- furniture, clothing, services, cars, artwork, etc. A "financial contribution" is specifically a donation of money.
Donations are sometimes called "gifts", albeit ones with certain conditions and sometimes benefits for the giver.
Donations are also sometimes referred to as "support" to further emphasize that you are helping in some way.
Any of these are acceptable:
Thank you for your (charitable) donation
Thank you for your (financial) contribution
Thank you for your gift.
Thank you for your support
Lastly, there are certain specific kinds of donations, which you can thank someone for if appropriate:
endowment: A grant of money providing for the continuing support or maintenance of something.
grant: a donation given for a specific purpose
bequest: a donation given posthumously in a will
In certain limited cases you might also use something overly positive like beneficence, benefaction, or philanthropy, or somewhat negative like dole or handout.