A laptop is useful for many courses, although not absolutely required. A mac is no more useful than a typical laptop, and debatably less useful in many situations. They're also obscenely expensive for no benefit. Depending on what you need, you can get a cheap little netbook/similar from e.g. Lenovo that will suffice for general browsing and reviewing of materials from VLEs etc, and an external HDD for storing any work on. I have a nice one for work that I got from JL (although I think it turned out it was cheaper from Lenovo directly) that was about £180-200 which is perfect for browsing etc and can even run less intensive games (such as league of legends) in min settings. If you need to keep large amounts of files on it permanently, or intend to do some more serious computational modelling, then something a little more robust may be better, but there are plenty of options available.