Can I legitimately participate in an activity or eat something? The question takes me down a line of law. Paul however turns the attention to our attitude towards God for it.
They forbid people to marry and order them to abstain from certain foods, which God created to be received with thanksgiving by those who believe and who know the truth. For everything God created is good, and nothing is to be rejected if it is received with thanksgiving, because it is consecrated by the word of God and prayer. (1 Timothy 4:3-5NIV)
All things are created by God to be received by us with thanksgiving. In giving thanks to God we consecrate the item – set it aside in our hearts for God through His word and prayer. The limits are where we cannot give thanks, either because of prior conditioning or because it violates our first love for God.
This takes the focus away from whether it is good or bad and on to our attitude towards it. Can I receive this with a thankful heart? Romans 14:22-23 develops this –
Blessed is the one who does not condemn himself by what he approves. But whoever has doubts is condemned if they eat, because their eating is not from faith; and everything that does not come from faith is sin. (Romans 14:22-23NIV)
In this passage Paul is concerned about what is suspect to some believers. If I cannot receive it in faith then I leave it. Thanksgiving to God is a good indicator of faith to receive.
adaringfaith 
Thank you Derek.
Might I suggest that there is another constraint which Paul highlights in the verses immediately preceding those you have highlighted in Romans 14, that although it may be legitimate for us to eat / drink / engage in a particular activity which is not proscribed by scripture, and which we might on other occasions receive with thanksgiving – nevertheless we need to be sensitive to the possibility of putting a “stumbling block or obstacle” in the way of another believer (Rom 14:13).
This is particularly relevant when relating to those from other cultures than our own.
Hi Ian, sorry I missed this one. Yes, I agree, this is a good point. It is interesting that the principle continues around the idea of love. The love of God and the love of our fellow man.