Can I file expenses incurred in 2018. My wife passed away in July 2018 from cancer??

So sorry for your loss.  Unfortunately, the cost for funeral or burials is not deductible, so you cannot enter that.

Because she passed away in 2018 you can still file a joint return for 2018. 

  That way, you will get the married filing jointly standard deduction of $24,000 (+ $1300 for each spouse 65 or older)  which will lower the amount of income you are taxed on.

In My Info, you will need to indicate that your spouse died. When her name is in My Info,  there is a screen early in the interview that asks "Do any of these apply to [name] ?’” where you will do that, and then a drop down will appear where you can enter the date she passed.

If you have dependent children still living at home, you will be able to file as a qualified widower for the next two years after this tax return.  Post back if you need further help.