How many months?
It depends if child is walking etc.
Big activities that take up 1hr+ could be playgroups, classes like monkey music, swimming, going for a long walk, feeding the ducks, storytime at the library/choosing new books or CDs (never to early to start reading).
At home you could make music with saucepans and wooden spoons/various other kitchen utensils, put in some music and dance/sing, do clapping rhymes, play with sock puppets.
Peekaboo advancing to hide and seek (you only pretend to hide your eyes!) or making a den out of a big box to hide in
Messy activities: finger (whole body) painting, water play, gloop, cooked/dried pasta, baby safe homemade playdough, tearing/scrunching up paper
A treasure basket is a great idea for that age for 20 mins or so at a time and you can rotate the items round.
A good routine will help the day go faster, and I definitely recommend getting out the house to something each day, and if you're stuck for activities think of skills you want them to develop/the next developmental stage and how you can work on that.