Congratulations on your up and coming wedding!!
Centre pieces can be anything you want! ..
Flowers, if you look online you can find some cheap websites that do silk flowers and would look lovely in a vase.
Wilkinson's do cheap vases as do Primark!
Balloons are fun to have..
Candles (if you venue allows) a trend seems to be candles inside vases filled with colourful pebbles/beads or a vase full of water with floating tea light candles.
A cake stand full of mini cup cakes..
Bowls full of sweets always go down a treat.
For entertainment you could have a magician, a dj, a band, a face painter if you have lots of children! ..
At our wedding we will have a lot of children there so I'm going to make up party packs for them with crayons, colouring books and what not.
Hope this helps
xXx