If the sheriff officer has an attachment order, they are entitled to take any goods from outside your home unless they are exempt. The majority of your possessions will be exempt from seizure, as it is recognised by the courts that you will need them.
If non-exempt items are stored in a garage, for example, and the bailiff gains entry, these goods will probably be seized and subsequently sold. Your car may be at risk, as well as any other types of vehicle stored outside, such as a motorbike or a bicycle.