Great Western Coffee Shop

Intending travel FGW on Friday 1st August to Brighton, returning Monday 4th August.
Like the thought of HST to Paddington & like the thought of much coffee with some food thrown in.
Thence First Capital Connect to Brighton (no coffee or food, but would have had enough from the HST)..
We could however change at Westbury & use FGW to Brighton.
What stock is used from Westbury down, and are there coffee/food facilites onboard, please? 
Never used that section of line, so that's into the unknown for us.

Returning last time cross London resulted in much sweat lugging cases & not finding an Oyster at Farringdon; thence the trek at Paddington.
A lovely Super Guard sorted the fevered brows on the return HST - thank you.

Note to mods - please move as applicable

The FGW service from Westbury to Brighton on a weekday is currently diagrammed as the SWT Class 159 hire-in. No absolute guarantees that it'll be running on the day in question, however it is supposed to be with FGW throughout the summer. Every time I've been through Bristol Temple Meads on a weekday morning in the past few weeks the SWT 159 has been running up to Great Malvern at 0841. This then returns from Great Malvern through Bristol to Brighton, departing Westbury 1327.

One bonus of this unit being used by FGW is that the 1st Class sectioned is declassified throughout its daily use.

There should also be a trolley catering service onboard, although this isn't guaranteed.

One final word of caution. The FGW Brighton service is far too regularly affected by problems on the network or staffing issues. Often turned round short of Brighton. The last time I'd planned specifically to use the evening return FGW service from Brighton I discovered that it was cancelled from Brighton and had actually been turned round at Westbury due to staff shortage.

If it's walk-up fares that will be purchased then the via Salisbury option will be cheaper. You can chose to travel to Bristol and pick up the Brighton service there, or change at Westbury.

How about changing at RDG & GTW?  Benefits of HST for the majority and avoiding London

Many thanks to bignosemac & old original for very useful information.
It looks like the London option will be more secure, so will either tube it to/from Farringdon (or St Pancras International) for the FCC to Brighton.

Thanks gents, appreciated.