When it comes to toddlers and outings be consistent.
If at all possible, limit errands to morning time and make only one or two stops.
Bring along your own drink/snack and small toys to help distract him.
Praise, praise, praise him for being a good boy on the errand. Start as soon as you put him in the car to go, then from the car to the stroller/cart, on the way into the store etc. (assuming he's not pitching a fit).
Finally, try to engage him in what you're doing: give him a picture book with foods if you're grocery shopping, or his own "shopping list", ask him what color things are etc. to take his mind off things.
at 8:13 PM on Feb. 1, 2009