I'm not sure you have to go out and buy burial plots if you are relatively young...you never know what life might bring in terms of divorce, re-marriage, moving to the other end of the country...or another country...there are so many variables. Maybe you'll want to be cremated, and just need a small niche for your urn, instead of wanting a whole plot.I think as you start to get older it might be a good idea to finalize your thoughts and put a plan in place. I married my second husband when I was 46, and we bought two beautiful places in the outside wall of a mausoleum overlooking a river--gorgeous. And much cheaper at that time than now, of course. It was a relief when he died to know that we had that beautiful final resting place that we had picked out and paid for. It was certainly one less thing to worry about during an incredibly stressful and difficult time.
The one thing I think you should absolutely do early is discuss with your spouse what you want in terms of your final arrangements: cremation or burial, big funeral, small funeral, any special requests for funeral, green burial...whatever. I'll never forget that when a friend's adult son committed suicide, my friend started pulling together a conventional funeral with a casket, burial, etc. Then the son's friends told him that the son had not wanted that--that he had said he wanted cremation with ashes scattered...needless to say, my friend brought his preparations to a screeching halt and put his son's wishes in place. Good thing he found out in time.