Be lazy on purpose for half the day. Some of the MOST fun I've had with my son in our entire life has been in PJs with french toast or popcorn or brownies for breakfast. Tickle fights on the couch. Snuggles with a movie. Bouncing on the bed.
Ordinary things, that just turn extraordinary, because it's all about us instead of needs must. Whipping off my belt and using it as a tow rope in IKEA (him being toed about on his knees just laughing and laughing). Having a cold bubble bath in the middle of a hot afternoon. Twice. Riding a particularly long escalator up and down 40 or 50 times in a row. Painting with shaving cream on the bathroom mirror. Going somewhere with a piano. Buying feeder goldfish. A long drive in a hot car (we constantly have to find indoor activities, because it's COLD and wet here... in your case, an air conditioned car). A big chunk of it getting on and off the exit of the freeway (because the circle is fun). Reading books in Barnes & Nobel to find the "best" one for silly voices (that was our criteria for picture books, best 'voices' for mommy to make). Getting "coffee" at starbucks (he loves strawberries and cream frappucinos). Going for a ferry ride, just to feel the wind (aka go 'there' and back again, but never get off the boat. Dig out the halloween stuff and do face painting. Wear a halloween costume to the grocery store in summer. Never change out of a bathing suit that day. Blow bubbles. Go to a dress rehearsal of a play or opera. Bring our leftover breakfast brownies to the local fire department.
I spent all of my son's early years dead broke. Life can still be pretty fun and special spending nothing to $3 for "coffee".