If it's at all research-related, you likely should not be paying for the item with your own funds. That includes software, textbooks, laser pointers, society memberships, conference travel, and so on. When in doubt, ask.
If you would like to purchase an item, the easiest way to do so is through the Prime Marketplace. Note that most tech items need to be purchased through B&H or CDW-G. Otherwise, Amazon Business is a safe bet. The procedure is as follows:
Add your item(s) to your cart
Send Andrew a screenshot of your cart and ask for a chartstring to use
Assign the cart to Jacqueline Armstrong and in the message include the chartstring and state that you are in the Rosen Group
All relevant university policies apply for any purchases you make. In general, all physical items you purchase with research funds should, by default, be considered to be "on loan" to you while you're in the group. That said, in general, you will be allowed to keep most personal use items (e.g. laptops) upon graduation when possible.
Using software without the proper license for research-related activities is strictly forbidden. If you need something, just ask! Don't worry about the price.