Accumulating sets of materials over time is a good approach to gathering science materials. That way you don't end up with boxes of materials that don't meet your students' needs even though they looked so useful in another classroom or a catalogue. But pipettes/droppers and magnifiers are "must-have" science tools!
There are many, many cute ideas on Pinterest--to help evaluate their potential for scientific learning, see this article on how to choose quality effective learning experiences: To Pin or Not to Pin? Choosing, Using, and Sharing High-Quality STEM Resources from the NAEYC's journal, especially the list of reflective questions "Considerations for selecting high-quality STEM experiences for early childhood classrooms."
A Reuse & Recycle center is a good place to get materials such as sea shells and fabrics, and nature is a wonderful source of materials that inspire close looks and questioning, leading to investigations to learn more.