Could these 2 FTSE 100 shares help me retire comfortably?

I’m looking for FTSE 100 stock to buy to help me retire in comfort. Could these two blue chip shares help me achieve this?

A high-risk FTSE 100 share

There’s a lot that I believe International Consolidated Airlines Group (LSE: IAG) has going for it. It owns established brands like British Airways that are popular with travellers. It has exposure to money-spinning transatlantic routes. And despite its failed attempt to acquire Air Europa the business also operates in fast-growing European low-cost segment through its Aer Lingus and Vueling divisions.

It’s impossible to talk about travel stocks like IAG without discussing the Covid-19 crisis. And as things stand this remains a big concern to me as an investor. Today reports emerged that British Airways will scrap hundreds of flights to US destinations Nashville, Baltimore and New Orleans due to soaring Covid-19 infections.

There could be much more disruption too as Covid-19 infection rates soar in many regions. The number of US cases has just hit a new daily record high of 1.5m. Also this week the World Health Organisation has warned that Europe faces a “tidal wave” of Omicron infections that could affect half of all Europeans in the next couple of months.

Debt worries

This is particularly concerning for IAG given the huge amounts of debt it has to pay off. It had €12.4bn worth of net debt on the books as of September, and it may have to accrue even more before the pandemic is over to survive the crisis. Shareholders should be braced for the possibility of fresh share placings that could dilute their interests, too.

It’s also worth remembering that such high debt levels could seriously undermine IAG’s growth plans and its ability to exploit industry opportunities like the highly-popular budget segment if it comes though the crisis.

Banking on Bunzl

For these reasons I’d much rather invest in Bunzl (LSE: BNZL) shares instead. In fact this is a stock I’ve already bought to try and build funds for retirement. I like the broad range of essential everyday products it supplies across many industries. The goods it sells include wound dressings for hospitals, packaging for supermarkets’ fruit and veg, and hard hats for construction sites.

Bunzl has its fingers in many pies and it does what it does across many territories, too (it works in some 31 countries in total). This diversification by product, sector and geography gives it exceptional profits stability. And as a consequence it provides supreme peace of mind for me. There’s good reason why Bunzl’s grown the annual dividend for 28 years on the spin.

My only concern for Bunzl is that its acquisition-led growth model could see it run into trouble. This could be, for example, if it overpays for an asset or a company fails to deliver expected returns. That said, I’m encouraged by the FTSE 100 firm’s strong track record on this front. It’s why I’m considering buying more Bunzl stock for my portfolio today.