Carry some balloons in your bag and if your toddler or child is getting fussy blow one up when you are out and this will keep the peace! Also it doesn't take up as much room in your bag as toys would!
If you are heading out the door and you don't have any wet wipes or you cant use wet wipes as your kid has sensitive skin, take a travel bag with some wet face cloths in to wipe any mess away through the day. This also saves you alot of money not buying wet wipes.
Download games such as puzzles and educational apps on your phone so when you are going to be out and waiting a long time you can help distract them.
Carry a few items in your bag such as stickers and a couple of pens and a little notepad for them to scribble on.
If you are heading out somewhere like to a restaurant or somewhere that will require them to sit still for some time, make a quick stop off at a playground before you go so they get most of their energy out and then it will be easier for them to sit still while everyone eats.
If you are going grocery shopping, load your bags of food into a washing basket when your home. All you will have to do is one trip from the car to your house.
Keep a bunch of random toys that your child hasn't played with in a while, store them away in your car and while your travelling in the car let them go through it. This seriously helps so much for us as our little one hates car rides.
Pack a tonne of snacks and a lunch box even if you plan on eating out as you never know if they are going to like what they are served and its good just to have a back up plan.
Bring your pram even if your child is not going to go in the pram and this way you can use it to push along all your bags and things you may buy while you are out.
No matter how old your kid is always pack them a spare change of clothes and a jacket even if its sunny that day the amount of outfit changes we go through is crazy with all the puddle jumping and food spilt. If you have space it also pays to bring yourself a spare change of clothes to in case you get mud and food on you too.