Do the best that you can. As one person, you are not going to be able to fill the lack of a father; but, you can reassure your children that you love them, are there for them, support them; and, are doing the best that you can. Set the best example you are capable of for them.
My children went through school wearing clothes that I had either made myself or bought at the local thrift shop. I included the girls in the decisions made such as: "Would you like extra lace on the nightie I'm making for you?" or "Would you like this outfit better than that outfit?" I tried to let them make as many decisions about as many things as possible; not, just their clothing.
For entertainment, we hit the free swim at the local pool a lot; we went to the park with a picnic lunch; we went hiking; and, mainly we spent a lot of time together.
However, I think the most important thing I did then and still do is that everytime we say good-bye whether in person or on the phone, the last thing we said to each other was "I love you." If anything ever happened to either one of us, I wanted the last words we said and heard to be "I love you".