Well, you don't have to - as I realised when my little daughter (15 months at the time) showed me how much fun it could be!
When you have your toddler in your trolley, use his/ her signing ability to play games with the food you pick up.
Where is the milk?
When choosing the items which your toddler can do the sign for (ie Milk), ask him to help you look out for it as you go past the shelves (Sign WHERE MILK)
Pick up the cheese instead and ask/ sign "Milk?"
This gets your toddler to feel he is helping you choose the shopping and it empowers him also to choose items for himself (within reason!)
Baby can shop - game
I encouraged Hannah to show me the signs for the things she saw on the shelves - and I put in the trolley whatever she signed...this made her sign frantically all the way throug the shop much to the amazement of other shoppers.
Of course you then have to find a way to get rid of all the unwanted items before you get to the checkout!!
See your shopping trolley as a teaching tool and your toddler will not have the chance to get bored!