Absolutely yes!  The package of flower food is a balanced formula of ingredients used to feed your flowers, to treat the water and to aid with the free flow of water up the stems. 

Research has shown that cut flowers that have the water changed every 2 days and are fed floral food - perform better.
 

Gerbera straws are used to give a little extra support to the head of the flower and to eliminate neck bend due to the weight of the head against the hollow like stem.  Decorative wire can be used as well.
 

An angle cut on the stems of flowers assists in providing more surface area of the stem to the water which helps the flower drink water. 

As well, an angle cut keeps the stem end from sitting flat against the bottom of the container which could stop the flow of water up the stem.

When choosing sympathy arrangements we use the following as a loose quideline

for an immediate member of the family - casket sprays, wreaths and standing sprays, for more distant relatives standing sprays, wreaths, baskets and arrangements are lovely

for a co-worker or friend - baskets and arrangements are more than appropriate, as well as gourmet or fruit baskets

colour on the other hand is strictly a personal preference, calming and serene, bright and cheerful or somewhere in between - all are acceptable as sympathy arrangement colour schemes