Can I give my executor(s) some monies as commission for their services?

In Singapore, the court can at its discretion allow the Executor(s) to be paid a commission of up to 5% of the assets collected by them.

Source: Singapore Statutes Online website, Probate and Administration Act 1934

It is not mandatory to put in your Will instructions to offer some commission as this can be applied by the Executor to the court. If you do specify something to be given to your executor, please take note of the following:

Your executor(s) may still apply to Court for a commission not exceeding 5% on the value of the assets collected by them.
This might make the Executor a beneficiary as well since practically you are giving something to him/her in your Will and thus he/she and his/her spouse should not be a witness to the Will.
Any fees arising from the process (e.g. accounting fees, funeral expenses, applying for the Grant of Probate) will still be paid out from your estate.

Giving to a definition (as compared to giving to a named personnel) runs the risk of disputes arising from differing opinions on what the definition entails.

Listing using broad categories can have serious downsides as they may still be ambiguous, overlap with other categories, and is often more prone to mistakes. Listing each personnel individually is still the preferred approach as it adds clarity, makes future updates easier, and helps prevent unintentional errors.

Similarly, both CPF and insurance nominations are not made to unspecified groups of people, rather you will need to list them down individually.

Giving a percentage of an asset and/or residual assets

In the system, you can add such a person / entity with the following configurations:

Full name:

Whosoever my executor(s), as commission for his/her services

Relationship:

Others

Within the system, as with any other assets, you can allocate it accordingly:

Giving a specific amount of money from an asset and/or residual assets

Giving a specific gift from a specific asset

Under the “Allocate Assets” tab, within that specific asset toggle on " Additional instructions" and key in the following:

I give whosoever my executor(s) a specific gift of {Currency}{Amount} to be drawn from this asset as commission for his/her services.

Giving a specific gift from your residual assets

Under the "Select Clauses" tab, toggle on "Other Instructions" and key in the following:

I give whosoever my executor(s) a specific gift of {Currency}{Amount} to be drawn from my Residual Assets as commission for his/her services.