To contribute to the blockchain is you can run your own node. If you wanted to donate then I suggest you donated to the developers who are trying to make bitcoin better. Holding your own bitcoin in my opinion should also be contributing to the blockchain since you are making a transaction and it should be recorded in the blockchain when it is confirmed. Using it in your business is also helpful for bitcoin since it is what satoshi made it for.
If possible, running a Bitcoin full node but it requires big storage space so if you can not afford enough disk space and other technical parameters for a Bitcoin full node operation, you can run a Bitcoin prune node.
Running a Bitcoin prune node and using it for your Bitcoin storage and transaction broadcast is still better practice than relying on nodes run by the others with SPV wallets such as Electrum wallet.
The Bitcoin Network with more information about Node Types and Roles on Bitcoin blockchain.