In your example, milk, you've seen yourself that it's gone up from around £1 to £1.10, which is far in excess of the CPI - so your budgeting needs to take into account the things that you actually buy, rather than the contents of the CPI 'basket'.
You also need to take into account as yet unknown pressures upon the manufacturing and supply chain of goods from Brexit, weather conditions affecting crops, political issues such as whether China is pissed off about something or is still in the acquisition stage of empire building and a whole load of other factors which, with all the will in the world, a figure which is used to show governmental 'success' in the previous year can't give you a fair indication.
Basically, if it's something you have no choice but to purchase, the chances are that it's going to go up by a lot more than CPI - so, food, electricity, transport costs, council tax unless there's a local election planned and the council is on good terms with Central Government, that kind of thing.
It might sound overly dramatic, but planning for a 5-10% increase in basic foods and household items is realistic for any given 12 month period. If it's too high a guesstimate, great, you have money left over to help with the other expenses that will have increased. Some retailers will try to avoid increasing the price visibly by reducing the amount sold - the 5kg boxes of Basics washing powder for £2.50 in 2013 are now 1.625kg for the same price, for example, and some headline items might be kept artificially low because people notice if they go up as much as the other items (piece of M&S thick cut steak that would do 4 servings was £10 six months ago, now £12.50, for example, or the £3 chicken in the Co-op has gone up to £3.95 or 2 for £7 in a similar time period).
Creating your own bespoke records and calculations will serve you better over time - that's why some older ladies have always recorded their shopping and the prices paid as part of household management; it allowed them to see over time and plan for future years based upon what they actually bought.