1 Acts 15:20
2 we can any time we want to. I have many many times. Some individually may choose not to, because like a lot of games chess is based on war strategy and we are taught to "learn war no more" (Isaiah 2:4), but that is a conscience matter, most (I believe) would just consider it a game.
3 Christian products? we can. I purchased a Bible (the Message Bible) at a local bookstore the other day. I don't have a need for other "Christian products" if you are talking about writings by so-called Christians. We have our own products we recieve free of charge and ahve no need to read someone else's opinion which we would likely consider to be false teachings. We have no need of crosses or symbols which we don't use in our worship and would consider idolatry.
I have used Strong's concordance and have considered purchasing it, and Vine's works are often quoted in our publications so I would not feel strange about purchasing those things. Also I own a book (not written by witnesses) called "The Two Babylons". I don't consider it to be completely accurate, but I glean from it what seems to be historically accurate and archealogically sound. We actually have sites run by Witnesses that sell items such as multi-translation Bibles and interlinear Bibles that we sometimes purchase things from. As well as things for our ministry such as bookbags. etc. So yes we CAN "purchase Christian products". We are just very choosy about which of such things we own. We don't wish to mix truth with falsehood.
4 "God bless you" is actually a superstition. I've read two explanations of where the custom came from. Neither of these two explanations are consistent with our beliefs. the first explanation is that it is based on the idea that ancient man believed that the soul escaped and wandered around while a person was sleeping or that it could escape whenever someone had their mouth open. So saying "God bless you" when someone had an involuntary reaction such as sneezing prevented the devil from "snatching" someone's "soul". We do not believe that the soul is a separate entity within us but that we ARE souls. So there is nothing to snatch, and no need to be superstitious about it.
The other explanation I have heard is that the Pope ordered people to say "God bless you" when someone sneezed during the time of the Bubonic Plague because so many were dying right and left that he figured many would die without getting the "last rites" said over them. This way they would be "blessed" before they died in case that was coming. We don't believe that last rites are necessary, but feel that is one way the Catholic church has used to obtain money from people. We also don't believe in "hell" as a place of torment, so people are in no danger of going there when they die so no need of that blessing. How a person has lived their life, whether they have been obedient to God or not and the sort of heart condition they have had all of their life will determine whether they recieve a resurrection or not , it is in God's hands what will happen after they die, and no "bless you" on our part will change that.
5 Boxing, wrestling, martial arts are all fighting sports. We are taught to be "peaceable with all men". It is not consistent with Christian ideas of love your neighbor or love of God for us to be learning to hurt other people.
6 Join clubs or sports teams? I assume you are a young person in school? We don't encourage our children to get involved in social events that will put them into too much contact with non Witness youths. They do not share our values, and the Bible clearly tells us that we should associate with those who love God because in doing so we will develop good habits that will keep us close to him. It isn't that playing sports is wrong or even joining clubs that meet during regular school hours. It is that we don't have the time for such pursuits usually because they tend to take away valuable time we need for other things such as Christian meetings, the ministry and study and family time.
7 Pray in the presence of men? Not exactly accurate. A Witness can pray silently in front of anyone without a head covering. A Witness can pray out loud in front of men who are not Jehovah's Witnesses. I had a study with a man and I could pray over that study. However if a brother accompanied me on the study I would either ask him to pray or I would cover my head.
This is based on scriptures in the Bible where the apostle Paul tells us that he does not "permit" a woman to exercise authority (within the congregation) over a man.
The Bible clearly tells us that there is a headship arrangement. God is head over all, then Jesus. Beneath that is the men in the Christian congregation then each man's wife, beneath the wife is their children. As Witnesses we respect the headship arrangement.
1 Timothy 2:11-14, 1 Corinthians 11:3-16, Ephesians 5:23,24