I'm starting a repetition with my students in 5th grade after they learned in elementary school how to sum up larger natural numbers (also 5- to 6-digits) by writing down that calculation. 

As introductory example that has a connection to their every day life, I search for a good exercise that just needs them to add up several natural numbers without being too easy. 

I thought about an amusement park where there is a roller coaster and the park needs to calculate the degree of capacity utilization but am lacking a formulation that is consistent and just needs them to add some numbers up, since a decrease of the number of uses forces a subtraction.
Do you have a better idea?