The fore-blessing (bracha rishona) must be said where you eat.  However, sometimes you may begin eating in one domain and continue eating in another domain. A domain may be any physically limited area (car, house, restaurant, office building) or the outdoors (highway, park, etc.). Once you left the first place, you are considered to have had an interruption of thought (hesech da'at) and are no longer eating that original snack or meal. 
Whether you say a new fore-blessing depends on your intention when you said the fore-blessing:

• Do not say a new fore-blessing if you had intended to go to the second place, as long as the food at the second place is in the same food categories as what you already blessed on at the first place.
• Say a new fore-blessing if you had not intended to continue eating in the second domain, even if you had planned to return to that first place and continue eating.
  Exception You do not need to make a new fore-blessing if:

  • You return to the first place and even one person who was eating with you is still there, OR
  • You had eaten bread or mezonot and then left but had not said the after-blessings of birkat ha'mazon or al ha'michya, even if no one is left from before.
    Reason Since you are required to say birkat ha'mazon or al ha'michya, you are still considered to be continuing your meal.

    Note As long as you are under the same roof, do not say new blessings on food at the new place (such as when switching seats or even rooms in a restaurant).

    Exception Even if you washed your hands and said ha'motzi at the first place, say a new blessing on food that would have required a new blessing at the first place, such as new wine or any dessert other than mezonot.