When it comes to shipping to Spain aspects such as firearms and ammunition require permits for them to be brought into Spain as do antique items. It is possible to also ship food and alcohol as long as they are shipped in moderate quantities. If you are trying to ship large amounts of food and alcohol they may be confiscated.
In the case of customs regulations and shipping to Spain, the customs regulations only apply to shipments that are coming from outside of the European Union (EU). Some of these regulations are household goods, which may be imported into Spain without paying duty, this is provided they have been used and are imported no later than 12 months after you have obtained a residence/work permit. Shipment arriving after this deadline requires additional formalities and will be subject to extra expenses and delays. Most probably its VAT and duty-free admission will be denied. Duty will be applied to new household goods and any such items found within a declaration of used household goods will render the whole shipment rejected for free admission.
If you wish to ship your motor vehicle to Spain there are certain documents and information that you need to have in order to do so. The shipping of motor vehicles to Spain require the Title or Registration documents as best proof of ownership and time in use. Liability insurance on automobiles must be valid at time of import. The import of your motor vehicle is duty/tax free provided the owner obtains residency within Spain. This is valid for driving for 6 months after which you must apply for Spanish registration. On registration you will be required to pay registration tax (rate is 13% of CIF value).
You are allowed to bring your pets across to Spain if you so wish as part of your shipment. Your pets do not have to go into quarantine provided that they have had their current vaccinations and you have the certificates to prove that they have. It should be noted however that quarantine may be required for unusual pets. 
