Have you any idea of where you would like to go for your holiday? Have you any experience of walking in that sense?
Saga specialise in holidays for the over 50s and although expensive is usually excellently catered.
Other independent companies provide guided walks with different overnight stops - luggage transported for you - or from one hotel or b&b, and transport to different starting points.
Where you go and the time of year will determine the gear you need - walking boots are a must, and the sooner bought the more comfortable they will be. No need to pay silly money (some are several hundreds of pounds) but �60 or so should get you adequate breathable, waterproof boots.
Goretex jacket will be breathable, waterproof and windproof and goretex overtrousers will keep your legs warm and dry.
The cost of goretex has fallen in last few years so you should be able to get a good jacket for around �50 - maybe less in the sale.
And comfortable trousers, shirts and jumpers should see you through - jeans and sweatshirts if you wear that sort of thing. Comfort is the most important.
A small but sturdy backpack will carry your drinks and lunch.
Can we have some idea of where you'd like to holiday, the time of year and your expectations?