grab some sandwich at river. vs grab some sandwich on river.

Some examples from the web:

• Grab some goggles and a mask.
• When you were born, I got a deli sandwich at the hospital cafeteria.
• That's because I wolfed down a steak sandwich at lunch.
• The Franklin Sandwich at Denver Biscuit company.
• Busted while trying to shoplift a $6.00 chicken salad sandwich at a Pennsylvania market.
• I'll just get a sandwich at the café.
• Because I always have a sandwich at my hairdressers.
• Maybe he made the sandwich at home.
• I once had a very undercooked fish sandwich at a parade.
• You had a sausage and egg sandwich at midnight last night.
• Now grab some wood and pipe down.
• I wanted to grab some paperwork first.
• I came by to grab some paperwork from the truck.
• I'll go grab some menus for you girls.
• I'm going home to grab some clothes.
• Come in here and grab some of these eggs.
• Maybe after your jihad, we can grab some steaks.
• I thought we could grab some breakfast.
• - Come on, Ramiro, grab some.
• MK, grab some uniforms, re-canvas the streets.

Some examples from the web:

• I'll ask Inara to look in on River.
• I see that today's lesson was to be on rivers.
• Last night, he got a bullet in the neck at the skate park on River.
• (Police radio chatter, siren wailing in distance) Last night, skate park on River.
• Now, tonight, we are staging one of our important races, between the car, public transport, a bicycle and Jeremy's rather fanciful belief that we should travel everywhere on rivers.
• This issue does not only concern the Member States in question, because there are also Member States downstream whose installations are sited on rivers.
• Grab some goggles and a mask.
• Now grab some wood and pipe down.
• I wanted to grab some paperwork first.
• I came by to grab some paperwork from the truck.
• I'll go grab some menus for you girls.
• I'm going home to grab some clothes.
• Come in here and grab some of these eggs.
• Maybe after your jihad, we can grab some steaks.
• I thought we could grab some breakfast.
• - Come on, Ramiro, grab some.
• MK, grab some uniforms, re-canvas the streets.
• I thought you were just going to grab some aspirin.
• Give you a chance to grab some coffee.
• Grab some guns and ammo from out front.