A doctor’s bag, an iPad, a can of Red Bull and a football bootbag have all been stolen from insecure vehicles in Grantham over the last week.
Thieves have stolen items from 20 vehicles in the last seven days simply by opening a door.
Sunglasses, wallets, cash, laptops, drills and a lighter are some of the other items stolen.
Thieves also broke into a Volkswagen Transporter, stealing tools from inside.
Gary Stewart, inspector for Grantham, said: “If you leave your car or van unlocked your vehicle is a sitting-duck for thieves who will rummage around for literally anything of value and sometimes they will take trivial items too.
“Thefts of this nature are incredibly frustrating for the victims and for our officers investigating as they can be simply avoided.
“Please check your vehicles are always locked and remove anything that could make you a target – it isn’t worth taking a chance as you could become the next victim.”
Any suspicious activity should be reported to Lincolnshire Police by calling 101.