Is there a way, in Magento 1.9.1 CE default, to prevent certain products to be shipped to certain countries? Or should I use some custom extensions?
If you're asking what I think; you want to ship to, for example Canada, but certain products, such as from specific manufacturers can't be shipped to Canada.
You have to either rewrite the checkout process or get an extension. Amasty has one that worked well on one of my sites, but was around $100 - totally worth it to avoid me messing up the checkout.