I've bought only 4 concert tickets, but there are 5 of us. What shall we do now?
Let's... / Why don't we...? / Shall we ...? / How about...? / Why not...?
This weekend, we are going on excursion to another city. What shall we do to pass the time on the bus?
Why don't we...? / Shall we ...? / How about...? / Why not...?
