My youngest is 19 months. This is such a fun age.. I remember having tons of fun all day when my son was this age, too. Any craft stuff... construction paper, safety scissers, stick glue, scotch tape, paint, markers, crayons, chalk... put a box of stuff on the table and let him go at it and create and experiment. The 'results' probably won't resemble anything but it's the process that counts... eye-hand coordination, etc. Teach him how to cook. My kids could make their own PB&J sandwiches all by themselves by 18 months. (plastic knives are good). I make cookies or breads or something like that several times a week and the kids love to help. My 4 year old can do most of it all by himself... I just read directions and put stuff in/out of the oven. The 19 month old can measure, pour, crack eggs, mix with spoon/whisk, get ingredients from pantry, etc. Make a list with pictures and go for a walk to find those things... a scavenger hunt. Do it indoors if it's too cold, otherwise just bundle them up and head outside. Playdoh is a big hit. For more fun, have him help you make it first. Water play or sandbox.... fill a big plastic storage bin with water or sand and put it in the kitchen (or other non-carpet place). Put a tarp or something under it if you want to help with cleanup. Then let them pour and dig and play. Or just let him pull up a chair and play in water at the kitchen sink... he'll like to 'help' you wash dishes.
If all else fails, toddlers love 'helping' with housework... separating laundry, putting clothes into washer/dryer, folding towells, matching socks, putting clean silverware away, washing windows with squirt bottle and paper towell, holding dustpan when sweeping, etc.