You will have to check your local regulations at your institution. (my answer is based on my experiences at public US universities and companies)
Tax code may also be important in determining what items you can expense, both for yourself and your institution. For example, in the US you can deduct certain costs related to having a "home office" as business expenses. But if you play video games in your office after hours, the whole thing is void! Similar restrictions apply to other possibly dual-use items, such as a car (may be a business expense, but the rules for reimbursement change to those involving business use of a personal vehicle if you use it for anything that isn't business).
Tax law is relevant to expense reports because your company/institution is probably treating those costs as expenses, and therefore they are not taxed as income. If you use anything for personal use it becomes a type of income and must be taxed, even if your institution wanted to provide it. In that case, they would have to not only provide you with an expense reimbursement, but also add the amount to your income, withhold taxes as appropriate, etc (of course this system could vary greatly by country) - this all seems like it would be quite a bother, and if I were an administrator I wouldn't be too happy if a post doc, or full professor for that matter, made me go through all of that for 60 euros.
In my current institution's policies, there is a list of exclusions for business travel expenses. The item on that list that applies to your situation is:
Statement of Policy
Following is a list of expenses which are not payable/reimbursable with university funds. [...]
Personal items and services, (e.g. toiletries, luggage, clothes, haircuts, etc.)
I tried to find some information on business travel in the Netherlands, but I was only able to find information about allowed reimbursement amounts for transportation, lodging, and meals, which may suggest that those are the only categories commonly reimbursed, but it may also suggest that there is more freedom for specific institutions to set their own policies. Also I don't read Dutch, so I was limited to documents that were available in English.
If you had a institution-owned computer, you might be able to justify the purchase of a carrying bag for that computer (but not cash reimbursement for wear on a bag you purchased previously), but not for a bag that carries your personal items like clothing, etc. If this was permitted, it would probably be purchased for you or reimbursed the way you would be reimbursed for other types of equipment, not through the travel reimbursement procedures, and the bag would be institution property, so you would be leaving it behind with your business laptop when you leave the institution.