We've all experienced upselling and cross-selling before — whether it's a side of fries to go with a burger or upsizing a coffee order to unlock a bonus promotion.
One trick you could try is to trigger an upsell or cross-sell when they reach a certain cart value. For example, if they're at $80 and they need to get to $100 to qualify for delivery, trigger a $20 upsell item. That way they get to $100, plus more!