In Eurostar you get a light meal in standard premier wich you can use with your 1st class interrail. Business premier with meals is excluded from interrail. Keep in mind to reserve a seat soon enough.

From Brussel the ICE trains to Frankfurt and there a change to Munich no meals included, some light meals in DB lounges at train stations in Germany. Same for Eurocity to Italy. 

Nightjets (2nd class only train), you get in sleeper cars a la card breakfast and in couchette car a light breakfast. 

On Frecciarossa trains in Italy you get some snacks and a drink/coffee/water in business/first

DB First class lounges Do Not admit interrail pass holders.

As above, nowhere in mainland Europe provides the same level of included food service the 2 main UK intercity operators do, a snack and free tea/coffee is the limit in most countries. However many IC trains  do still have a restaurant/bistro car with a decent selection of meals at reasonable-for-on-board prices.

In general do not expect anything for free-this is not the UK.

In the german ICE there is at seat service-so you do not have to stand up and go to overcrowded bar-bistro-car, conductor will do this, after the usual round of checking the tickets, but normal prices are payable (not cheap-but many german frequent trainrider has a kind of status and then gets some coupons for the odd free drink). That is also why the 1st cl pass is only 25--30% higher in pirce as 2nd-whereas normally 1st is well over 50% more.

In DE and AT are also lounges in all main towns-in DE you canNOT use this with pass, but in AT can-do not even have to show special REServ or whatever. Since just a few weeks the lounges of DB are also sub-divided in like silver/gold-without/with some snacks-but again; NOT for passholders.

My experience last month travelling interrail first class.

trains:

Thalys: cold meal and royal amount of additional wine due to delays 

AVE (Spain): light meal and drinks 

RailJet (AT): free drink of choice 

Regiojet (CZ) free water and juice

EIP (PL) cold meal and drink 

SJH (Sweden) breakfast before 9, coffee, fruit and cookies during day 

Denmark: coffee, fruit and cookies

Italy: soft drink of choice 

Lounges

AT: snacks and drinks 

Sweden: light meal buffer and drinks

France: coffee (only if you’ve loyalty card in addition to interrail)

DB: good food and drinks in premier lounge 

(only if you’ve loyalty card in addition to interrail)

MAV (Hungary): decent meal a la carte and drinks 

In a lot of other trains just a free cookie and or water 

@jtim the free drink on railjet is only in business class wich is 15€ reservation fee, in first class (wich is lower than business on a railjet) you get nothing.

@Angelo completely correct, worth mentioning. Business class was the only thing left on my train to Munich.