I am in the same situation, and here is what I do: I buy things like a rotisserie chicken at the grocery store for dinner, it's about $7 and I stretch it to 2 days (1 leg and quarter for kid on one day, one breast for me, next day, same thing). I then look for veggies or other side dishes that are on sale, usually from the frozen aisle. I can get one of those steam veggie bags for sale for about $1, and that comes out to about $4 a day in dinner. I get apples and cheap snack puddings for dessert, or whatever is on sale in terms of fruits and puddings. By the way, Wal-Mart sells Banquet TV dinners for $1 in the frozen aisle, so that's another option. Sometimes I will get the foot long sub at Subway for $7 and split it with my kid. She thinks of Subway as a treat.
For lunch, I pack myself a peanut butter sandwich. Again, this is very economical because a large jar costs me about $5 and will last me over a month, and the generic store-brand loaf of bread is usually about $2 and lasts me for weeks. I will save a night or 2 a month to splurge and go to a restaurant with the kid, as a treat, and to motivate her to do well in school. Other than that, I am spending very little on a daily basis. I get the regular gas, and in terms of cleaning supplies, I buy those at the dollar store, for a dollar each. This is also a decent place to get some cute kids' gifts. Funny thing: my daughter has liked some of those crystal making kits from the dollar store more than some of the fancy gifts she got from others, because it was something we could work on together. Speaking of fun activities, bike riding through the park, flying a kite on the beach, going to free movie screenings (and there are quite a few in Miami this time of the year!), are all fun, inexpensive, family-oriented ideas. I also check Groupon and LivingSocial for zoo discount vouchers, animal encounter vouchers, and other events and give those as gift to my kid. She loves them! Last year, I got a speed boat ride for 2 for $20 on one of those sites and she still talks about it.
I buy a lot of my clothes on eBay, secondhand, for as much as $5-$8 for a top, jeans I buy from Ross or other discount stores for about $12 and keep those for years, sometimes I buy them at Wal-Mart too. I only shop when I need to (jeans got holes, shoes are too worn out to repair with shoe glue or polish, kid needs a sweater...), and I try to sell a lot of her toys or other things we no longer need/use on eBay or craigslist. Books are also purchased secondhand from half.com, or amazon.com.
I try to find a hair color that makes it easy to go without dyeing often, so I can spread that out to getting a root retouch and a trim once every 4 months, unlike most people who go every 3 weeks to touch up their roots. You can also dye your hair at home and go somewhere like Supercuts to get a trim every now and then. If you just get a trim, no layering or styling, these cuts are about $12. My co-worker goes to the Vidal Sassoon, Paul Mitchell Academy, or beauty schools and gets her hair dyed and cut for a much lower price than most people pay. I do my nails maybe 3 time a year, and the rest of the time, I trim them and polish them at home. Again, these services are sometimes offered very economically on Groupon or LivingSocial, and you can treat them like a splurge for yourself.
In terms of cable TV, I have free cable and I also have Netflix for $8. I don't need the premium channels, pay per view, or some of the fancy TV packages they try to push on me, no DVR either. I am barely home anyway! Honestly, if you get Netflix and you cannot get free cable where you live, Netflix is MORE than enough. They have great movies, documentaries, indie films, foreign films, TV shows...my friend got rid of his cable and internet and saves about $70 a month that way. He has data on his cellphone and at work, so he does not feel he needs to get internet at home too.
Lastly, try walking as much as you can. It saves on gas, parking expenses, and gets you healthy.