1) Is this a necessity or a want? If not buying will negatively affect your lifestyle, then its a necessity. If it is, think it through and tell yourself whether you have done a thorough price comparison with similar items. If it is a want, ask yourself whether you can delay it.
2) Is it worth foregoing a chunk of your investment money to buy this? Big ticket items will usually dig into your bank reserve/investments which are actively collecting interest. Do you love this item so much that you are willing to forego precious interest for it?
3) Is there a substitute for this item that you can think of? Most retail items are easily substituted with cheaper alternatives. Do not get blinded by flashy advertorial exteriors. Reduce it to its simplest form/function and see if it is still worth your money.
Hope these questions can be of help to you when you make your next purchase.