I use monster cards and pick the ones I'm going to use before the session. There are several decks available, 1 with NPC and beasts, a deck with CR 0-5 monsters from the monster manual, a CR 6-16 deck, a epic deck with CR 16+ legendary monsters, a Volo's deck and a mordenkainens deck.

Here's the basic decks that I use:

https://www.amazon.com/Monster-Cards-Bundle-Including-Challenge/dp/B07KJFS9VM

https://www.amazon.com/Dungeons-Dragons-Spellbook-Cards-Accessory/dp/0786966947/ref=m_bmx_dp_l12fqjgo_sccl_2/137-0689768-2733636?pd_rd_w=wx1dE&content-id=amzn1.sym.a0d2d03d-ec86-4ddd-96c5-f96776301548&pf_rd_p=a0d2d03d-ec86-4ddd-96c5-f96776301548&pf_rd_r=8MPW1XWH2FZ4QG4R58KC&pd_rd_wg=wadZP&pd_rd_r=9814bc05-3da4-4ea3-ab00-a3181642b23d&pd_rd_i=0786966947&psc=1

There are also spell cards, a deck for each class, a deck for racial abilities and feats, a deck for magic items. Spell book cards are really useful to give to your players so they aren't constantly flipping through the manual looking for their spells.

https://www.amazon.com/Spellbook-Cards-Arcane-Dungeons-Drangons/dp/0786966548/ref=m_pd_aw_sbs_vft_none_sccl_10/137-0689768-2733636?pd_rd_w=QIE1q&content-id=amzn1.sym.f69f8dfb-6db4-48ed-9773-fc959de76f50&pf_rd_p=f69f8dfb-6db4-48ed-9773-fc959de76f50&pf_rd_r=33CFWKPKS8HX11FM54PV&pd_rd_wg=nyurM&pd_rd_r=dd20b617-128e-4c41-907c-fca80d616c65&pd_rd_i=0786966548&psc=1