One of the best investments ever for my child is a clear plastic tote/box from wally world that is 7inches deep and 15" x 24" and comes with a lid! That is her sensory box, we still use it daily and my daughter is four! Oh and get an apron too! This will help her keep occupied and help her sensory development and let you have some time for yourself for a little bit. My daughter would normally play for 15-20 minutes when she was 2.5 so you can get some free time!
Suggestions that are more toddler friendly are:
Make a batch of instant pudding directly in it
Fill it with water and a little play boat, measuring cups, funnel, spoon
Squirt some dish soap in it and fill it with water making tons of bubbles!
Make ice cubes, you can add food coloring to make different colors and throw them in there (my daughter would wear mittens because she didn't want to directly hold the ice)
Make a large batch of jello and put it in the box with fun kitchen utensils, like a potato masher!
Give them flour, cinnamon or whatever nice smelling spices you have in your cabinet, give her a little bowl and whisk and measuring spoons (whatever you got in your kitchen drawers) and let them pretend to cook
Cook spaghetti noodles (you can dye if wanted) let cool add tongs bowls cups etc.
I have a little preschool science set with big plastic beakers and I fill them all with different colored water (just add food color) and I let her pour and mix and make new colors! (You could just use plastic cups instead of beakers)
Cornstarch and water makes OOBLECK! It's amazing and fun, when you squeeze it, it becomes a solid, let it go and it becomes a liquid. (Add food coloring to change it up.)
Flour and one of those sifters!
Sand with a small bucket, shovel, sand molds, seashells
They have these water beads which are "supposed" to be nontoxic if swallowed but if your little one is still mouthing things use tapioca beads because those are edible
I make playdough (add 1 cup flour and 1/2 cup salt to nonstick pot, then measure 1 cup of water (mix in food coloring directly into water first) then add colored water to pot and stir, heat on medium for a couple of minutes then flip mixture over and cook other side for a couple minutes until its not liquidy, I normally put it in a bowl to cool for a couple minutes then knead to make the texture uniform and done! Store it by rolling in a ball, if you put it in a bag it will turn liquidy
Dye noncooked rice with food color (just put in a large ziploc bag and add food coloring and quickly mix it and then spread it in tub let it dry for 15 minutes and your done, then you can reuse it again and again!)
You can also dye noncooked pasta (For pretend soup: I would add a pot, pretend veggies from her play kitchen, and ladle, and bowls)
Once she's older you can also do things like:
microwaved ivory soap
shaving cream (w food coloring)
slime (the one with liquid starch and glue is really good)
scissor practice with old magazines and ads
fill it with lots and lots of pom poms
or lots of feathers
It keeps her attention long enough I can pay the bills, or load the dishwasher without constant interruptions, I set it on the dining table and let her go to town! Another bonus a lot of the activities let her get out her need to dump and pour in an appropriate setting, and they all help her sensory development.