Task is not related to product backlog. Task is related to sprint backlog. Activities you described are not tasks.
When we plan our next sprint we always reduce planned capacity by all holidays and trainings. We also reduce capacity by "administrative overhead". In our case administrative overhead is usually 1MD per team member per week. This overhead is for meetings and possilbe assistance in maintainance on already deployed projects.
Edit:
I think you should never create tasks for meetings, presentations, etc. in your spring backlog. Why? Because each task has some estimation wich affects current sprint. During sprint tasks are completed within real time and based on that burndown chart shows team progress in delivering customer value. What value will customer receive from meeting? Moreover such task is probably not related to concrete user story so what progress will be visible in product burndown chart? How you decide how many user stories should be taken for the next sprint when you have to count with value not included in their complexity (story points)?
Adding such dummy tasks (tasks with no added value) to your sprint backlog will also affect your velocity. It will look like each story point costs more than in reality because meetings time will be included in real work.
What type of meetings do you want to add to your sprint backlog? SCRUM needs only few meetings - daily meeting, planning meeting, review meeting, retrospective meeting and in larger project SCRUM of SCRUM. Daily meeting is so short that it doesn't have to be included in planning. Planning meeting, review meeting and retrospective meeting don't have to be included in sprint. SCRUM of SCRUM is specific and it doesn't affect whole team - can be reduced from planned capacity of attending members. No more meetings are needed. Most important: Communication needed for completing task is part of task estimate.
If you need other meetings simply reduce your capacity. If the customer, management or Product owner complain about small capacity simply explain them that it is because of non standard administrative or bureaucracy overhead.