From the time my daughter was a baby, I have been doing something my mother-in-law calls "Toy Recycling." It was easier to do when she was months old, but I still use this tactic to some degree. "Toy Recycling" is a great way to decrease boredom, increase brain activity, and save money. I takes some effort, but not much, and really keeps my daughter engaged.
When my baby was about four months to twelve months old, I kept some of her toys in a closet. Every month or so, I would take the toys in her closet out for her to use, and put some play things she had out away. Bringing "new" toys into her world every month was exciting to her, and she gained a new interest in old things. Also, being at a slightly different developmental level each time she played with one of her toys, she used them differently, and therefore formed new thoughts and skills.
At about a year old, my daughter started to ask for certain toys or activities, and I felt it was inconsiderate to put her toys away at an older age. Also, at this point, she had too many toys to even keep track of, and hiding some seemed like more trouble than it was worth. Rather than hiding toys, I rotate them around the house. I change the location of her toys, books, and dolls. For example, my daughter has a doll house. Sometimes the doll house is in my bedroom, and sometimes it is located in my toddler's playroom. There are also spots for her books in our living room, my daughter's playroom, and her bedroom. Every so often, I grab a few, and rotate them to different bookshelves in the house.
I find that "Toy Recycling" keeps her interested in her play things and books, and gets her to think of new ways to play with the same toys. For example, when I brought the doll house upstairs, it made my toddler use rooms of her doll house that she was not interested in before. Not to mention, keeping a toddler interested in the toys she has, means buying less toys. Since holidays and birthdays only come twice a year, stretching toy enthusiasm definitely helps save money. Spending a little time each month rotating toys is worth the rewards!