It "scares me" a little bit when I read about using vegetables or coke bottles........sorry I do not mean to judge......but why not just go buy a nice butt plug or dildo? Much safer and hygienically clean...
Any way....if you start playing with your ass using smaller butt plugs and dildos you can "train" your ass (and your mind and body) to being anally penetrated without pain. It will take some time (weeks or months of regular anal play). Use lots of lube....take your time......and let your ass get used to being opened up.....learn to relax and control your breathing.....eventually you will get to the point where there is very little pain, and your ass begins to crave the feeling. You will also be able to "experiment" with different size dildos, different position for being penetrated, different lubes.....how deep? how fast? how big? We're all different....but at some point you will begin striking and rubbing your prostrate....and things will start to feel really really good....like nothing you have ever felt before.....you'll know it when this happens....it feels that good.....
And yes...like many others have said....finding a partner to top you.....find a caring, experienced guy willing to take his time with you at first.....anal sex can and should be very pleasurable (in my opinion) rather than some painful experience...when done and experienced in the right way.........good, pleasurable, intimate anal sex will give you the most powerful and fulfilling orgasms that will change your views and perspective on sex. Hope this helps....it's my experience.....