As suggested by Mike you can write a trigger to copy the data from one object to another. However if you are looking for a more generic option then you could create a custom setting in ur org to define the field level mapping between opp and the custom object and then use a apex class or trigger to dynamically copy the record from opp object to ur custom object.
Edit the Account layout and goto Text Subscription related list. Click on setting icon at the right corner of the related list and add the field which you need
Best Answer
The are System fields on most objects:
Here you will find all standard salesforce objects:
Standard Objects
Each object is linked to the detail page where all of standard fields of the standard object stands.
For example Account:
and so on.