I'm going to buy
I’m going to buy something to eat.
Surveille mon sac pendant que je vais acheter un ticket.
Watch my bag while I go buy a ticket.
Je vais acheter du vin, je reviens.
I'm going to buy some wine; I'll be right back.
— Quand passent les cigognes (1957)
Je pense que je vais acheter un de ceux-là.
I think I’m going to buy one of those.
Je vais acheter la première tournée.
I’ll buy the first round.