In the US, at least, the IRS frowns a bit at people over-using business deductions.

Fair, tax laws are different everywhere. Your mileage may vary.

"Any new gadget or widget" might be deductible if your business includes, say, reviewing new gadgets and widgets. If you're a software developer, though, kitchen gadgets--for example--aren't generally considered deductible. In fact, if you're a software developer, very few things are.

The magic is in how you justify the expense as part of the business. Nothing stopping you from putting crappy reviews online for everything you buy and then deducting your life expenses.