If you're expecting, don't look at must-have baby lists. What you must have is a carseat, safe sleeping arrangement, and the other nessecities that babies require.
Everything else, decide as you go along if you really need it. We purchased almost all our kids' clothing secondhand or received things as hand-me-downs, then donated or trashed or handed down everything as soon as they grew out of it.
Invest in experiences, not toys, as much as possible.
A zoo membership or a toddler music class or a day at the science museum.
Even though we've done this, the toys accumulate. Put them on rotation. One third "favorite" toys that are always out, one third rotating toys on the shelves, one third rotating toys in boxes in the garage. Avoid a toy bin, keep toys on display so they always have a place and can be found to play with, but also so you have a sense of what's ready to get rid of.
For gifting holidays, the Rule of Four. Something you want, something you need, something to wear, something to read. Keep toys simple, open ended stuff like blocks, Lego, art supplies.