Can I include in my taxes just 1 line item, for example "office supplies (yearly sum)" and list the total amount, or do is it best to list out each individual line item?

You can just enter the total for each expense category.  So yes just enter the lump sum total.

Just enter the total in each category as a single item. And you don't have to say "yearly sum." It's understood that the amounts on your tax return are totals for the year.

There are predefined places to enter certain common types of business expenses such as office expenses. Don't make up your own category for expenses that fit one of the predefined categories.

Keep the receipts or other detailed records with your tax records so that you can show how you got the totals if you get audited.