When I started out I was mocking up packaging with paper and scissors but as I progressed I used a Cricut craft cutter. Everything had to be scaled down slightly for my box sizes, but it was a great way to test the look and feel of a box, as well as test user experience when it came to opening the box - was the text the right away up on the lid? Was the card thick enough or too thick?
It's a lot easier now with all the templates available online, especially the virtual mock up software - but make sure you test physical usability which virtual mock ups can't do.
Top tip - take a printed box and set it on a shelf in the supermarket - does it stand out?
Share your packaging in the comments below and let me know how you make mock ups?
Cricut machine: https://amzn.to/4qDC2uP (Amazon affiliate link - I use the Explorer 3 but I would recommend third party cutting mats, not the Cricut mats, they're like superglue 😅)