Is there a way to introduce mandatory checklist in a catalog Task without any customization?

[Slava Savitsky]

No, out of the box there is no possibility to make checklists mandatory. To be honest, I would not recommend doing so even if there were a technical possibility. Typically, trying to force people to use some functionality with technical measures only creates resistance. If you make checklists mandatory, some people will simply start checking off the items without actually performing the corresponding action, which is not the result you want to achieve.

[Bill_Collins]

Dee255 That depends on your definition of a "Check List."  BTW (Slava) requiring fields is simply a part of process and what SNC is all about, i.e., forms driven workflow.

I would not want to modify the sc_task form, which is where I'm guessing your question is coming from.  Add your required fields as variables on the cat_item.  These could be "checkboxes."   Hide them on the cat_item.  Set them as mandatory on the sc_task with catalog ui policy or client script (assumes you have variable editor as field on form).  If you want greater fanciness, use a Business Rule on the sc_task table to control when the variable is required and pop info messages, e.g., field must be populated before closure.  Of course, this can get a little messy on the sc_task table as the BR has to be generally specific to the cat_item of the RITM.