If you have any specific funeral requests, then it is important to set them out within your Will. If you have no close family members, this can be a good way to ensure that your wishes are carried out after you are gone.
If no direction as to funeral wishes can be found, then your executor will have to make the decision on your behalf, which may not otherwise reflect what you wanted. Some people feel very strongly about a burial or a cremation, and whether they would like a religious or non-religious ceremony and this is the ideal place to state those wishes.
Your executors are able to use your own funds to pay for your funeral but you can also look into taking out a funeral plan to ensure everything is paid and taken care of.