EWTN Catholic Q&A
Doing things on Sunday
Question from David Lannoye on 10-24-2012:

Is it a sin to go shopping or going to a Mall on Sunday?

Answer by Richard Geraghty on 11-09-2012:

Dear David,

It is not a sin if one have taken care to go to Mass in order to worship God, thus fulfilling the Church's law. If shopping and such leads to missing Mass, there are sins involved. Missing mass without a serious reason is a serious sin.

Dr. Geraghty