The one supplement I always have in the pantry, and recommend to all and sundry, is fish oil capsules. There are reams of evidence for the health benefits, but is another I recently discovered.
Typically, muscle mass decreases 20% between the ages of 40 and 60. In a trial of women given 4 grams of fish oil daily, in addition to weight training, after 12 weeks those women showed greater strength gains than women given a placebo. Because fish oil supplements promote muscle protein synthesis in response to amino acids and insulin, it is believed fish oil might delay muscle losses in older adults.

On another note, my brother is a landscaper which involves length hours of physically demanding work, rain hail and sun. He finds it a struggle to maintain weight (and muscle) due to the increased caloric needs of being so active. I know, hard to sympathise!
He asked me whether he should be eating white bread instead of brown and not worrying about
plenty of KFC and McDonalds. As far as bread, both are carbohydrate rich and relatively equal in terms of calories, but wholegrain bread is a better option for fibre and as it has a lower glycaemic index, it has longer-lasting effect on energy levels. Fibre is essential for healthy digestion - keeping up the grainy bread, vegetables and fruit is vital.

Bonus info! Beetroot is high in nitrates, which have been proven to improve blood flow, energy levels and endurance. You could gulp down a beetroot juice after your workout, or if you're not so keen, add some to your lunchtime sandwich or burger. Recipe for beetroot dip at Edible Urban Garden in Sydney.

As far as KFC and McDonalds - it's not really the calories that are a concern, but the high salt and saturated fat content. Both are serious enemies of heart health and because they are so high in salt and sugar, are unlikely to satisfy for long, leading to overeating and dehydration. If it's a couple of days a week, not too much of an issue, but if we're talking more than 3 out of 7 days? That's a habit to kick.