Here are a few:
Intentional speeding, for example, 75mph where 70mph is the speed limit.
Not grave, assuming good traffic and road conditions.
Underage Alcohol Consumption, no driving, drunkeness, etc.
Quite possibly grave, because this can lead to all sorts of sin, as well as to alcoholism.
Intentionally parking where it is illegal to park
Probably not grave, unless you’re causing someone serious inconvenience, anger, or danger (e.g. parking in a fire lane, or parking blocking someone’s driveway).
Sneaking into a second movie without paying (this one may be immoral for other reasons)
This is stealing. Because of the dollar amount of the movie, it might not be grave, however if you make a habit of doing that, enough venial sins can add up to a mortal sin.
If you’re talking about crossing the street carefully where there is no crosswalk, and being respectful to car traffic, it’s probably venial. If you just run out into traffic and make other people slam on their brakes, causing danger, that would be mortal.
The word ‘grave’ is a bit subjective and for cases where it’s hard to say if the harm to others is minor or serious, it would be best to consult your priest in confession.
Just my layman’s opinion

The book “The Faith Explained” by Fr. Leo J. Trese gives lots of examples of different sins and knowing which are grave or venial, and I recommend the book to you if you want to get a better understanding.
These examples have been easy because most of them fall under moral rules, not just legal. If you’re talking about laws which have no moral implications, then you would have to look at the punishments given out for breaking the laws, and decide whether they are serious punishments like jail, huge fines, criminal records , being taken to the police station (grave) or minor punishments (warnings, traffic tickets, misdemeanors).